Been there done that.
Advance offers a lifetime warranty then changes their part number on said part. So when, not if you need a replacement, they give you a 1 time replacement since they no longer carry "that" part.
Just got an A/C kit (compressor, drier, orifice valve) from Rock Auto for $139. Four seasons brand so middling quality but my "lifetime warranty" (Advance Auto) compressor lasted a year if that. Blown compressor seal.
Key to any reliable R12 to 134 change is flushing everything you don't change very thoroughly. The old oil will mess up the new system in no time.
Most parts I have taken back to Advance have been that way. It's a lifetime "replacement" not lifetime "replacements".
As long as you use Ester oil in your conversion it will work fine without a thorough flush. If you want to use Pag oil, yes you will need to flush it very good to get the old r12 oil out.