&&When driven warm at medium RPM
&&(which means it happens only on vacations, in the mountains) the oil
&&pressure warning comes on and stays on. It only happens after a half
&&hour of driving and the mechanics insist that they absolutely cannot
&&duplicate it however detailed instructions I give them. I first saw it
&&the day after I picked it up new in 1985, and since it has survived for
&&10 years, 

A friend's 1985 Golf did a similar thing, as did my brother's 1984 GTI, 
both after using 10W30 oil during respectively hot summers.  The Golf 
sounded horrible--the engine made a horrible clackety-clack noise.  Well, 
after a fresh dose o' 20W50, the noise literally went away as we let it 
warm up.  This was confirmed by an authentic and archetypal old-guy 
mechanic--he said, "Them Vee-dubs, they need the thicker oil"

Well, anyways...

JKH--New Mexico