Yes R134 came in with the early 90s.
So this vehicle probably was factory built with R12, although I encounter many cars of that era that have been converted to R134, sometimes successfully, sometimes not.
Different lube spec for the compressor also is a consideration between the two types.
Hoses and seals too.
If I planned to keep that car for a while, I think I’d just replace everything and be done with it. Evaporators can be a bitch to replace on some cars though.
Yes it was R12 to begin with. Now 134A. I suspect this IS the problem.