My two cents,
       My '90 AC that I installed in my '85, with an '87 compressor, wasn't
worth crap for years.  R-12 is way too expensive -- forget it.  I converted
to R-134a, and enlisted the help of AMA, who are here in Phoenix
(http://www.ackits.com/).  They know what they are doing, had my system
working fine.  They have more efficient replacement fans to pull more air
over your condenser, making cooling easier.  They are a good bunch of guys,
you can get good advice from them.

By the way, old hoses do leak through the walls.  Kind of a seepage thing.
New hoses have a barrier in them.

Good luck.

Bill Marshall
mostly '85 GL
Phoenix AZ