Mazda e 2000 van 1986 new motor{16000 KS}

I have unfortunatly had a recon motor put in by a bodgy fitter 30 monthes ago with 12 months warranty. It went back 20 times with oil leaks at every place possible now even the front oil seals leak now they wont look at it {? Possibly positive crank case pressure} and it now misses badly on pot 3 when idling, ive done tappets, inlet mannifold new gasket {was loose}, plugs, leads, dizzy cap, vacuum hoses. When motor running I remove the oil filler cap and motor stops. Please help.