I had the head on my 87 Turbo rebuilt to correct leaking valve guide seals and low compression in cylinder #5. I retested the head after assembly and now have low compression in 3 cylinders (135, 125, 120 and 150 in the rest). I went to what I thought was a reputable machine shop but now I'm not sure. Is there anything special about the Supra head that the shop may not be unaware of? Has anyone else had similar problems with a head rebuild?