Blue smoker

Titan owner: Question for all and I hope somebody could help me out with this. 

I have a 2007 Nissan titan I’m the original owner I currently have 185,000 miles on it.  I had the 2 catalyst converters gutted out a few years ago because they were clogged from which I was told was because of the fact that the engine blows a lot of blue smoke out the tailpipe. 

Obviously getting an inspection to pass on this vehicle in my State is almost impossible yet I was able to do it 2 years ago. I was given an estimate to replace the front 2 Catalyst converters which are part of the exhaust manifolds at a price of almost $4000 dollars. My issue here is the engine smokes a lot every time I turn the ignition on and then it disappears while I’m driving. Since I am now past due on my inspection I can no longer reregister my truck in my state unless it passes inspection. I would hate to invest all that money into the exhaust manifolds/Catalyst converters only to have them clog up again. 

I was told by another mechanic that it is very common for my year titan to do that and I can simply correct that issue by merely replacing the valve cover gaskets. I was told that oil is seeping through the center of the gaskets and down into the spark plugs . I also have to change out my coil packs which on the average is one per year. The only noticeable thing is that some of the spark plugs are drenched with oil when I remove them. Does this make any sense to anyone that may or may have experienced the same situation that I’m experiencing ? If so what if anything did you do to correct this problem. Thanks. 

Intelligent Tinkering: Either your mechanic is muddled more than any professional should be or you muddled what he said. Rocker cover gasket leaks cause smoke and smell from the engine bay and below. Leaky piston rings and/or valve guides causes blue smoke at the tailpipe. You seem to have both going on, but the tailpipe is the real problem. If it occurs at start up and not later, suspect valve guides. If it's rings you'd know because high oil consumption. (White smoke at the tailpipe is running rich.) What is the oil consumption? And the oil pressure (which tells you how good your main bearings are)? That and some idea of the condition of the transmission and body will tell you if it's worth fixing the cats, with or without rebuilding the engine. By far the easiest thing to do would be to put in a known good engine, either a reconditioned under warranty or a take-off from a recycler that has low miles. That way you can do the cats and headers too and you'll get good rocker gaskets and coils with the new engine. But only if the rest of the truck is worth the trouble. One way to think about it is that a decent older second hand truck is worth at least $10, 15, 20K depending on the condition. You can get there by buying a truck, or by spending money on this one. If it adds up to less, either way, you're ahead.