PM Cujet and ask him for his opinion on this thread.
I'm not a fan of MMO and would never use it in an aircraft. Like others here, I've seen it used in antique aircraft and I've known people who swear it helped. However, there are a few points that might help clarify the situation. Maybe more importantly, if you find yourself in a field, when the MMO stops covering up the problem, the FAA will, A) find out you've used MMO, B) treat you quite poorly. C) point to a crash known to be caused by MMO.
First, if one is trying to "cover up" sticking valves with a top end lube, the only proper fix is a mechanical one. Typically, the exhaust valve simply needs to be pushed out of the guide and down into the cylinder, then the guide cleaned. Pull the valve stem up through the plug hole and clean it too. It's not that hard, does not take all that long, and the engine does not need to be disassembled for the job.
Second, today's 100LL contains less lead than it did yesterday. What we needed to do yesterday is not really needed today.
Third, Swift 94 is available in many locations. It's an unleaded, approved, aircraft fuel that is, in essence, 100LL without the lead. It's worth considering for engines approved for lower octane fuels. It will mix just fine with 100LL.
Here is how the exhaust guide is cleaned in place. It's really not that hard to get the valve back into the guide after cleaning. A wire with a "U" bend at the top, fed through the plug hole, and a small strong magnet will do it. Or if you really must waste time, pull the exhaust off and use fingers to position the valve stem through the exhaust port.
By the way, one can easily lap the ex valve doing this. But you must pull the exhaust for access to apply and remove the valve grinding compound.
Here is the wire and magnet "trick".
Oh, and just like in cars, more frequent oil changes will help prevent stuck or sticking piston rings. Don't go 100 hours between oil changes. Shell did some testing and found that 35 hours was the practical maximum for a healthy engine. At which point the oil was sufficiently contaminated to warrant changing. Unhealthy engines need even more frequent oil changes.
