Of all I have, the 312 Pennsy K5 SIT runs perfect. Smokes nicely and runs smooth and quiet. I only run the old stuff for nostalgic reasons around the Christmas tree. Just started dabbling in AF a few years ago thinking it would be something fun to repair. Between the e units and SIT, I found out it can be quite challenging achieving nirvana! No interest in the new stuff, modern O-gauge has already claimed every last bit of space in the house available!
Rich