If the 87' is like the 1988 kdx200, it’s a great bike.
My friend owns an 88’, it's never been rebuilt; he rides it all the time full out, and it still runs really good, you can tell it needs a full rebuild since it's hard to start when it's cold, but when warm it takes a couple kicks. For the amount that he's put into it (around $250 Canadian) on wheel and swingarm bearings, brake shoes/pads; the bike has caused him no grieve. Suspension is really plush like all kdx's, nice on trails especially with the nice low-end power. Handling is ok; the bike being around 220 pounds doesn't help. Overall it would be an excellent beginners bike, and for maintenance: just the usual: grease/oil and check for wear and play every so often. :)