My `89 had a little over 30,000 miles (which is about 49,000 km) when I bought it, and I switched over to the full-synthetic castrol automotive stuff with no problems whatsoever. The shifting action is *slightly* smoother than with whatever oil the previous owner used, otherwise I don't notice any difference... and I change my oil and filter every 3,000 miles (4,828km).
On my 91 750 I change my oil every 3000 to 3500 miles. I use Motorex 15/50 non-synthetic. Think I may try the fully synthetic next oil change. Got 25,000 on the clock but I think It used to be a race bike so who knows for sure.
<font size="2" face="Verdana, Arial">Hey, someone after my own heart!!!
Usually monthly during riding season. More often if I've really been wailing on it. What with Mobil 1 15w50 being so cheap by the jug up here now, not much excuse not to. Normally never go over 2000 km though, since this hobby has cost lots of $$$$ and the oil/filter combo isn't in the same league.