I, too, have a 1999 5210 MFWD which I bought with 850 hours about 7 years ago, now I have 1350 hours. I've replaced one battery and done all the fluid and filter changes at 1000 hours. I have not done the valve adjustment called for, does anyone have an opinion on that? Oh, and I did replace the seat cushions with stock, they're not cheap!
Tractor runs great. I added a Quicke Q720 FEL which is heavier than the JD versions, and I'm about to replace all 4 tires (ouch!) because the fronts are shot, rears leak calcium, and I'm upgrading to bigger and heavier duty tires which require appropriate, corresponding sizes when upsizing the front. Mime came with the 8.3/24 and 13.6/28 4 ply, too lightweight for my loader and applications.
I wear hearing protection when doing any actual work with it, but don't bother when moving it around or scraping the driveway.
I'm really glad I bought this size. I considered a compact, but due to their popularity they were about the same price and this is much more machine for my 20 acres. I foresee keeping it "forever." I sure like to look at pictures of bigger JDs but truth be told I have no need for more machine than this.
The biggest shocker of my story -- I bought this on ebay. By far the most expensive thing I've ever bought this way but it turned out great, and I even kept in touch with the PO for a few years afterward. It was a win / win situation. He got more than the dealer would give him on a trade-up (he picked up another 100 acres to farm so needed to go bigger,) and I got a tractor that I could sell now for more than I paid back then.