AC compressor, again

The first AC compressor in my 88 Silverado lasted for about 25 years. The second one maybe 15 months.

Now the third one is leaking after about two and a half years. They leak around the seals in the "clamshell."

Both of the new ones have been brand new AC Delco, not remanufactured.

My questions:

Am I having this trouble with the new ones because the system has been converted to R12?

Do I just have to change these every few years?

If I have to keep replacing them, does anyone offer a lifetime warranty?

All the parts stores have lifetime warranty compressors, but you gotta prove the system was flushed, the o-tube and accumulator were replaced, and a vacuum was drawn on the system.  Difficult to prove for a DIY, pain for a good AC shop.  

Maybe buy a cheap compressor and replace every few years?   I gave up on the AC on my old truck, so when I do have to drive it, I'm miserable.