The retro R134a kits list the oil as being compatible with the R12 oil. I replaced most of my lines, condenser, AC filter, Evaporator, expansion valve, o-rings and a ac filter switch (that was leaking).
Charged the system up to about 30 psi of 134a, which is about 80%, added a can of Maxi Cool and with the recirc on, the air is blowing about 48 degrees. With the recirc off, it blows about 55 degrees.
No problems and everything is good. BTW, I watched my local MB dealer quote a guy $500 to convert his system then proceeded to watch MB evac the R12, change the AC filter, a couple of o-rings, install some high/low side adapters then charge the system up with R134a from a large tank. All for $500.
Guess MB does not feel the need to do anymore when converting from R12 to R134A.