You are correct that some have a drain plug and some don't. The ones I have seen are a small bolt. They don't look like a drain plug as we know them.I recently performed a transmission service (fluid and filter change) on a 2016 Mercedes-Benz E350 Sedan with the 722.906 seven-speed transmission. Although I normally do not work on MB, this car belongs to a good friend of mine and he wanted me to work on it for him. I did my homework before doing this trans service and learned a few things which may be helpful to others. Parts Needed: 1) 6L of fluid (pan-drop only), 9L of fluid (pan-drop and torque converter drain) 2) Trans Filter (mandatory replacement) 3) Trans Pan Gasket 4) 6 new bolts for the Trans Oil Pan (one-time use, torque to 35 in-lbs + 180 deg) 5) Drain Plug Washer - Most 722.9 transmissions built after 6/21/2010 use the 236.15 (ATF134FE) blue-colored fluid. 722.9 Transmissions built prior to this date use ATF134 (236.14) red-colored fluid. I used the Genuine MB 134FE fluid, but RMEuropean (SSF) sells the MB-approved Fuchs 7134 FE fluid for the 236.15 applications and the Fuchs 4134 Fluid for the 236.14 applications. For the 236.15 applications, please do not use aftermarket fluid. The MB approved 236.15 fluids have a viscosity of about 4.4 cst and I did not see any of the "recommended" aftermarket fluids matching this characteristic. - Despite what you may read on various MB forums and even the Mercedes EPC, not all 722.9 transmissions have a torque converter drain plug! See the pictures below. On this particular 2016, I think the transmission uses a slightly different bellhousing design to accommodate for the external auxiliary oil pump (this car has start/stop). After rotating the engine many times (27mm socket) and looking thru both holes (the big round one on the bottom and square one on passenger side), no plug was found. If there was another place I should have looked, let me know. - Buy a Fill Adapter and a Filling Tank that has a shut-off valve. See my pictures below. I used Assenmacher's #ATF129 adapter for MB 722.9 transmissions in conjunction with their 5L Driveline Filler. Having a shut-off valve is important because it allows you to "hold" the fluid in the pan while waiting for the transmission to warm-up. - There have been multiple revisions to the 722.9 transmission oil pan and overflow pipe depending on the model year. The overflow pipe is either black, white or green and they are not always interchangeable without also replacing the transmission oil pan. However, most of the 2010 and newer transmissions will use the green overflow pipe. If your transmission has the green overflow pipe, the fluid should be checked at exactly 45C/113F. Other overflow pipes have different temperature guidelines, so please check the manual. Ideally, you need to have a scan tool that can read the ATF oil temperature. I personally used the Autel MS906TS. - In lieu of the tool, there is a way to get the fluid level pretty darn close. Note: this method only works if you measured the amount of fluid removed and the transmission was allowed to cool for a few hours while you worked. This is what I suggest doing: 1) If you only did a pan drop AND you started the work when the trans was hot, fill the trans with 5.5L of fluid with the engine off and enable the shut-off valve on your filling tool. 2) Start the engine and shift thru all gears. 3) Wait several minutes and the oil pan should only feel barely warm. 4) Proceed with unscrewing the fill adapter and allow for the excess fluid to drain; about 1/2L should drain out. This should leave you with about 5L in the oil pan. 5) Once the stream slows to a drip, re-install the drain plug with a new washer and you are done. (My experience was a little different since I used the Autel scan tool. Before I drained the transmission, the trans fluid temp was at 155F. The car was off and worked on for about 3 hours. After pumping in 5.5L of fluid and shifting thru all gears, the trans fluid temp was still at 96F. I waited about 3 minutes and the fluid temp climbed to 103F. So at that point I unscrewed the adapter and allowed for the excess fluid to drain to a drip. After the fluid was done draining, I "plugged" the hole with my finger until the fluid temp reached 113F and then allowed the excess fluid to drain again. Even then, only a very small trickle came out. To be safe, I added a few ounces of fluid at this point to confirm that the trans was truly full, and it was....since the little bit of additional fluid I pumped in came right back out. So, I am fairly confident in saying that if you "set" the fluid level within a few minutes of warm-up, the level should be very close to being perfect.) Sorry for the long post, but I hope this helps someone who wants to service their 722.9 transmission. The local dealers all charge about $600 for this trans service and the parts only cost about $200 (even less if you use the Fuchs fluid). To be honest, this service is actually quite easy if you do all of your homework beforehand. No torque converter drain plug was found thru the round hole. When looking thru the hole, all you see is the bottom of the torque converter. I saw a few spots that looked like welds over areas where a drain plug may have existed, but this car did not have the drain plug. Pan Removed Amount of fluid removed after trans was allowed to drain for 3 hours. Pan cleaned up and green overflow pipe reinstalled. There was very little sludge at 42K miles. Pan re-installed and filling pump/adapter connected. Trans "Oil Level Check" function in the Autel software. This picture was taken after I had put back the drain plug and had the chance to wash my hands, so that is why the temp was past 113F.