Anyone use a GOOD yet inexpensive oil injector for R-134a systems? I have had some over-charge situations where the relief valve opened and lost a copious amount of oil. I need to be able to re-introduce the PAG oil easily. Prices are all over the place yet they mostly look the same. I am seeing videos where these guys remove the schraeder valve on the high side, pull vacuum on the low side, jam a rubber tube into the high side port, and stick the other end into a container of PAG, sucking it in. Do they not realize moisture laden air is also being sucked in? Or do they know to deep vacuum all over again? Yikes!