I currently own a old (30+ years) JD LX178 and a 22 year old JD L110. The LX178 is a work horse, the L110 is a residential grade piece of junk. However, John Deere is incredible with their parts support and ability to maintain their products. Even the parts prices aren't astronomical when you consider the inflated world we're in at the moment.
My LX178 has the ability to drain and refill the K62 transmission but the L110 has no such provision for the K46. I have changed the K46 fluid once in the L110 at 500 hours by removing the axle and I used the same hydraulic fluid that my LX178 uses which is John Deere spec'd J20C fluid. Neither IHT has ever given me any problems whatsoever.
I mention this because a new mower,,, even a cheap residential grade mower from Lowes or Home Depot, will set you back $2500. That's a lot of money to spend on something that simply isn't necessary. You can repair or replace any item on the D160 for a fraction of the cost of purchasing a new machine.
If I were a budget director I would not approve the purchase of a new lawn mower when the old mower hasn't even been apprasied for repair estimation. Pulleys, belts, blades, etc., are all affordable and replaceable on the D160 and honestly, the newer stuff is NOT an improvement. One area that might take a bit of researching for repair is if the mower deck errodes or cracks from use. The JD mowers use 12 gauge steel and they're not on the level of a SCAG commercial. My LX178 required a weld repair to two errosions areas around to 1000 hour mark. The L110 had a broken bracket at 500 hours. These both were easily repaired by me and gave me something to do on a boring Saturday.
I type all of this because I personally don't think it would be a wise purchase to buy a new mower when the old mower is still working. And it's just my opinion but I don't feel that the X series of JD mowers is worth the asking price. They're pricier but not necessarily more robust. Evaluate the machine on data other than engine power and deck width. And remember, WalMart has JD Green and Yellow paint for $6.88 a can. Keep it clean and green!