Well, the regulator in this engine was mounted incorrectly and the chassis mount didn't offer any heatsinking for the triac. That is obvious from looking at it, yet Lionel had this locomotive THREE times and never corrected that. Since it came in for smoke issues, and they actually replaced the smoke regulator and mounted it the same incorrect way, I'd have to say they dropped the ball!
If you have weak smoke, the very first thing to check is the screws that hold the smoke resistor in place, they are loose in about half the locomotives I get in for service. Also, I change the 6 ohm resistor for the 8 ohm as the lower value overheats the regulator and causes premature failure. This was another Lionel recommended service, but wasn't done on this locomotive.
I don't think you're ever going to get MTH level smoke from this unit, but you can get decent smoke. Here's the Polar Express after the smoke unit maintenance.