Rich, just a thought here, if you paid to have the rear main installed, then the shop that did the labor to install it should be standing behind it, as in this second time should be a freebie............
Unless they made a waiver at the time, they should be doing the job again at N/C. That's the way I did business in the past, but who knows what kind of excuse people hide behind nowadays. It appears that the leak repair is deficient in quality, therefore it falls in their lap to make it right. When you are a garagekeeper, (automotive repair shop) you have a moral, and usually a legal responsibility to give the customer what they originally paid for.
Now that you own the smoke machine, I'd offer to let them use it to diagnose where the leak is. Unless you and the shop aren't on speaking terms I would think they'd agree to that proposal. Then there's a trust factor if you even want them involved at this point with the repair. The machine doesn't lie the crankcase is leaking without the engine running. As mentioned, crankcase pressure is going to exacerbate the problem.
Just thinking aloud here, but I obviously don't know the complete situation.