Toyota Repair: AC Retrofit, r 134 freon, r134 freon

Question
I have a '91 Camry and '92 Corolla. Both are in very good condition (low mileage for age) and the AC has never given me problems. But, I do know they both aren't working as well as they used to (only about 10 degree drop).

At this point, converting to r134 is really the only option. I was quoted $250 to do the conversion at the dealer. That price, assuming it is an accurate estimate, I can justify. But, do you think I am opening up a can of worms by doing the conversion? Sometimes it is better to just leave well enough alone.

Answer
It would make sense to retrofit to the R134 freon as the R-12 is not available anymore in the US and most other countries, the conversion is really simple, actually it only involves removing the old freon and replacing the service valves, in some cases it's recommended to replace the reciever drier unit. The r-134 freon is much cheaper, about $22 per lb versus about $80 for the R-12