I have a 30 yr old Hein Warner jack I bought for $40; it was blown. I rebuilt the hydraulic area, replaced all O-rings. The jack is excellent, but jack oil leaks out of the bottom port which has a 3/4" ? nut. I used a coppor washer and Hylomar on threads but that doesnt withstand the pressure, which I guess could be quite high. How I can seal the threads?