need a little help with Hondas

[The Masons]

I've got a couple of old Honda 250s 1975 XL and a 1983 XLR.  After sitting 
for a month or more the clutch plates on the '75 stick together.  As long as 
I remember this it isn't too much of a problem.  The bikes are in a garage 
on a hill so I just have to remember to start coasting down the hill before 
I shift into first.  They usually free up when I hit 2nd gear hard or hit 
3rd.  The bike does not see 100 miles a season, so I only change the oil 
every 2nd year.  The '83 is the opposite.  The clutch doesnot seem to 
release completely and it slips around 6000rpm. I have a gallon of Valvoline 
Synpower 100% synthetic oil I was going to try in these.  Do any of you know 
if this stuff is compatible with motorcycle clutches?  Or suggest any other 
fixes.  Maybe sell the '83 to Buerhle.

Jim