I had an '85 RM 250 for 5 years, then sold it to a youngster who rode it for 4 more years. It was a really good bike for me. No power valve, so top ends are simple. This is fully counteracted by the very complex "full floater" suspension linkage. Pull it apart, carefully, and clean and grease everything.
my kickstarter wore where it contacted the stop, have a welder lay a bead there -its aluminum- and then file it to shape. the rest of the bike really held up well.