8cfm airablo pump problems

I have an airablo 8cfm electric vac pump with cooler on it. Last year I had problems with it only pulling 22 inches of vac it's about 8 years old and has pulled 26 inches until last year.Oil seems to flow through it and relaxed the filter ever year. So recently I got a new rotor new vanes bearing and seals, replaced everything today and its still only pulling 22 inches of vac then drops to 20 dead headed. I'm going to check for leaks on the pump in the morning after chores but I was wondering if anyone else is has had this problem and how the fixed it thanks

So today I bipassed the oil cooler and dumper oil directly into the pump it pulled 25 inches for 5 mins and dropped back to 20 any ideas?

The problem has been fixed for anyone wondering I bypassed the filter blew out the oil lines and it works there was not enough oil moving through the pump the create a max vacuum hopefully that helps someone trouble shoot someday

If bypassing the oil filter makes it work, then maybe there is the possibility of the wrong filter on it. It might have the wrong flow capacity.