If it's a good compressor then I would rebuild it,I like the old stuff and it may be as simple as a broken ring but I doubt it. Do you use good heavy weight single viscosity oil or the el-cheapo stuff,if so maybe try some straight 40 weight or?. This won't fix the problem but it will reduce the oil usage unless the barrels/pistons are fu$ked up. Automotive machine shops generally rebuild comps., at least they do around here, may have to look for the right place in your area. good luck on the good old stuff, its all worth saving and looks great in your shop all painted and cleaned up plus just anyone can buy a 400.00 Nancy comp. Oh yeah, many mower engines/comp. pumps use those cheap *** "flapper valves" made of textile/rubber on the head and upper valve housing and when they go south "and they do", you'll blow sh%t everywhere. Good luck at saving a pc. of USA.