Just curious, is it HF that you talked to or ABAC/American IMC (manufacturer of these compressors)? As far as I know US General is a HF name brand. I assume it was the 866 number you called that is on the the compressor? My buddy had some issues with his compressor & when he called the 866 number he said they were not very helpful & didn't sound very knowledgeable at all. I wonder who the people are for that 866 number?
One issue that may arise with synthetics is that they will sometimes seep through an imperfect gasket seal.
Agreed, sythetic oils are known to be "slick". Generally it's not recommended to use synthetics in a "new" engine. I never used snythetic oil in any of the engine builds I have done for customer's. Only recommended switching to synthetic after the engine has been properly broken in. In some cases that could be as much (or more) than 20K mi before there are no more signs of blow by & burning oil is not out of the ordinary if it wasn't fully broken in. But this of course were automotive applications.
My buddy picked up the same exact compressor as me just after I got mine, also used. But he wasn't so lucky with his, his was newer than mine. He had a leak between the valve body & later found out it was due to a missing copper seal in between the valve bodies. Even with a head rebuild kit, there were still leaks from in between the valve bodies (also used synthetic oil). Having these similar issues with thin modified head gaskets, I always use copper spray during assembly. I recommended my buddy to do the same & it fixed the issue (so far). The stock copper seal is super thin. Copper gaskets aren't known to seal well without the use of orings (requires machining) & any imperfections in the fittment of the parts will guarantee slight leakage.
I've been running Amsoil ISO 100 Synthetic in mine with no leakage at all so far. I've been monitoring it closely after what happened to my buddy. Hasn't been that long yet but if I run into the problems I'll be sure to report back here. I already have a head rebuilt kit on hand just in case. The valve bodies in these italian made pumps are known to be a hit and miss in reliability depending on how old they are. My buddy's replacement valve bodies had some slight differences than his originals.
To add, most single stage compressors are recommended to be broken in by running the pump the for about 30 mins with the drain open. I've heard for two stage compressors this same break in method is not as effective & must be broken in with pressure to put a bit of load on the pump. Generally rings need to be broken in with cycles of temp rise & cool down. I know it's not an internal combustion engine but I would think break in would be a similar practice but take longer to break in. Although mine was a bit used, I ran some break in cycles with the original oil just in case anyway.
