replacing R12 comp with POE compressor

Had a job given to me today replacing a 1/3 hp compressor in a pizza prep table. The model numbers were identical except for one letter. Anyhow the new compressor was labeled for 134a so POE oil. The old compressor R12 with a handwritten R409a on the defrost clock. So my question what is the experience of folks here of mixing POE with mineral or alkabenzine oil? The person who gave me the job called the supplier and he said as long as it is not a capillary tube system you are ok.

Funny thing is a year ago I was given a job after the person who started it left - a compressor replacement. It was labeled R404a so I assumed (I know the joke) it was 404 but when I got there ( 2.5 hrs way in the middle of no where) found it was an R409a system. Not enough R409 on truck and thought I had the wrong compressor I turned around. Called the same supplier and was told with R404a it was low temp with R12/409 medium temp. Ok walk-in cooler. But was told to get rid of any old oil in the system or change the oil in the compressor or it could cause problems - gumming or something like that I was told - nothing about Cap or TXV. I drained the oil and added mineral or alkabenzine. As far as I know it is ok.

I am interested in knowing what the world community thinks of this

To make things simple the right compressor is coming.

To be on the safe side, I won't mix them. Co-cktails of oils are unpredictable.

EDIT: intruding censorship in a legit word.

If it was me I'd just fit it and recharge with R409 - it will run on mineral or synthetic. I have done this quite a few times with no issues. DONT fit it and charge with R134a though

the mixing of oils is going to be your problem.... waxing occurs if you mix mineral with poe...

http://www.isc.tv/pdf/refrigreplace.pdf

mineral oil mixed with POE oil will form thick sludge.
compressor will cease & may cause long term problems.
ensure proper oil for the job ... ascertain the refrigerant. do not guess.