I have 2 systems both with Vilter compressors. One is a 450xl, single compressor, the other uses two 350 es compressors. Both systems have been in service for 20 years. Even with rebuilt or brand new compressors installed I am getting oil past the seperator(s) and not returned to the crankcase(s) I think oil is leaving more when they are unloaded and maybe in so fine a mist that it's going right thru the seperator. I am wanting to adjust Hot gas bypass to allow more time fully loaded. Both systems have had numerous problems and lots of people working on them over the years. Too many cooks? no doubt. Any body have thoughts on tuning this to minimize oil losses?