low pressure with westinghouse 3YC

Pressure won"t build past 25lbs. Valve springs look good and not broken. may be worn. Air goes in and out of filter. small oil leak where high pressure piston bolts to main body. can not hear air leaks when I turn it off. Compressor is about 55 years old. Changed oil and filled to mark. Is it a major job to replace gaskets on both heads top and bottom?