Stuart,
Per your post a few days ago about squeaks , I'd love to know your easy fix
for the upper control arm bushings. Our last winters 'El Nino' storms left
my 87 GL with control
arm squeaks that no amount of WD40 or liquid wrench can stop. 
My 87 gl I've had since '92, purchased with 45k miles. This summer at 154k
miles had her completely rebuilt , as the oil consumption had slowly gone
from 2k miles per 
qt. oil to 800 miles per qt. The heads never did leak. My mechanic said
that the oil consumption was from worn valve guides only, as pistons,
barrels , and all bearing where still within standard spec. I've changed
non phosphate coolant every year , and ran Mobil1 changed at 7k miles. I
learned my lesson with the heads with my previous 84 GL, bought at 56k
miles and heads done at 75k miles. 
I've never heard of 'norosion' but I'm going to check it out.
Everything else works fine, the slider door as well, but it seems no amount
of tightening the joints stops the left and right mirrors from
impotence....
Cheers,
Jess Lopatynski
87 GL
85 GTI
89 911