1995 Cadillac Seville WHITE SMOKE

Is it running poorly? You either have a fuel pressure regulator that is leaking raw fuel into the vacuum line, or an injector that is stuck and passing fuel at full rate all the time.

I would say it is probably the regulator. Pull the vacuum line that goes from the regulator to the manifold, and check for raw fuel. Possibly key it up and check, if at first you see nothing.

You had not mentioned, is it using coolant? If it is using coolant, then it is most likely an internal leak. Excessive raw fuel will cause white smoke, and the raw fuel smell. An internal coolant leak will result in some fuel being unburned, and along with the smell you will be adding coolant. It will also be running poorly and misfiring, that will occur with the smallest amount of coolant in a cylinder.

If it is an internal leak, which I think you have pretty much confirmed, the repair cost would exceed the value of the car, if performed correctly. What happens, is the threads in the block end up degrading, as they are aluminum. The tension is lost, and the gasket ends up failing. The repair is to drill all the head bolt holes and install a steel insert called a timesert. This involves a procedure, and special tools. The approximate cost can be in the $2500 range. And then there are the other possibilities. If the engine has to be removed(probable method for a 95), there are considerations like having the lower crankcase sealed if leaking oil, and other incidentals that would save you labor to have done at the time. It is possible a mechanic will tell you there could be cracks and such as well, I have yet to see a crack in a Northstar in the 17 years they have been used. Is it probable? In theory, yes. Most likely it is what I have described. A person versed in Cadillac, will offer you about the same hypothesis.