compression tests are next to useless.only definative tests is compression leakage test,is garage equiped?working round this,get engine at full working temp,remove radiator cap and run motor with probe from exhaust gas analyser close to coolant filler neck.if it registers any hydrocarbons ur gskt gone.snapon also do a similar test kit that uses a reactive liquid ,detects very small gskt leaks.or coolant presure testing may show up gskt leaks.That aside have u considerd an injector leaking.systematicaly disabling each injector in turn may show up a change in smoke density for either posible cause,rather like pulling of an ignition lead when running to find a misfiring cylender.
caine
June 2008