When I changed mine over all I did was let the R-12 out and then put in the oil and fittings that came with the kit. About a year later the orifice clogged up. Replace it and that's all that I've done. Been running it about 4 years now.
If you are letting R-12 OUT then how could contaminants go IN? I think your A/C guy is full of BS and you should go somewhere else or just try it yourself.
