R-12 conversion to R134 ... BTDT? Any regrets? Recommendations?

[Dave Conner]

I've got three type 44's still running R-12 and all three need recharged.
I understand some people are buying a cheap DIY kit ($35) and retrofitting
to R134.  I'd like to hear from folks who did this and whether they would
do it again, etc.  

Two of my cars have only gradually lost their cooling effectiveness over a
period of 3-5 years, so I'm willing to consider having them checked out
and recharged with R-12.  The third car got a new compressor/dryer last
year and the A/C worked great, but over the winter seems to have lost all
the R-12.  I guess I blew it by not converting this one to R134 at the time
this stuff was replaced.  I installed the parts myself and had a local shop
charge it with R12.  They say they pressure (vacuum?) tested the system
before charging and it showed no sign of leaking.  They suggest that over
the winter the front seal could dry out due to lack of use and the R12
wouild leak out.  Everything may be fine if they recharging the sytem
because the seal would re-seal itself.  (hmmmmm...)  I'm skeptical because
this car gets the exact same kind of use as the others and they never did
this, and this one never did this during past winters.  

Dave C.