As its only one exhaust it means its only one bank of cylinders?
the car had been sitting about 4 years prior to my purchasing it so could be sticky valve.
The gearbox oil connected to exhaust?
I understand any work on the bowls of the engine will be a big job. Will need to be 100% sure on the fault.
Brake buster wrote:i would start with a general check of all fluids , and make sure they are correct level and not cross contaminated
next would be to do a compression check on all cylinders
this will give you a base line
the V12 valves have been known to stick ,
just for elimination , the vacuum modulator on the auto gearbox has a seal, if this fails ATF can be drawn up the vac line to the engine causing white smoke , this can be intermittent to start with then full on white smoke as the seal gives way completely ,
hope its a simple issue , as v12 head removal or piston ring replacement is a big job