Ingersol Rand type 30 scuba compressor

My compressor is a 1970 something model.  It began filling very slowly.  I took the 3rd stage steeple cylinder off and checked the rings.  After putting it back together it blew the oil seal on the crank shaft.  I then got a rebuild kit and replaced all rings gaskets and valves.  Put it back together and it built up pressure much faster but at around 2800 psi it blew the oil seal again.  I have rechecked all the valves and rings and it still blows the oil seal between 2500 and 3000 psi.  I don't know what else to do.  Any advice would be greatly appreciated.