Lionel 6-8307 Problems

You need to go through all of the cleaning & lubrication steps for these worm drive engines, which includes oiling the side rods as they drive the front six drivers from the rear two... oil all axle bushings, lubricate the motor bushings, & replace the grease on the worm.  Use modern synthetics for all of it for top performance.

I have this same daylight and took it apart to clean and lube with synthetics.

It still runs poorly, drawing 30-50% more watts for the same work when compared with 5 other locomotives I measured.

I thinking the worm gear engagement is poor causing high friction.  I need to tear it apart and maybe add or subtract washers to try and adjust engagement.  Keep this in mind as you're tearing it apart.

The drivetrain should be almost identical to a postwar 736 Berkshire.  I know that motor bearings on other locos from MPC's "Made in Mexico" era weren't the greatest.  Perhaps substitution of Postwar parts is the cure?  Motor number is 681-100.  If you also change out the chassis you'll have to paint the driving wheel rims white.  I've seen smaller postwar locos at train shows that were customized this way.  Careful application of white enamel using a Q-tip?

The Lionel service manual describes adjusting gear mesh on the 736.  It mentions adding shim washers, then states "if mesh is slightly tight in spots, run in the locomotive for several minutes."  I don't like that advice.  Either the mesh is correct, or it isn't.  If the bearings are worn allowing the axle to wiggle around, or the worm wheel isn't concentric, "running in" isn't going to cure it.  For this and other reasons,  I'm not a fan of the 736.  The worm should have been geared to the THIRD axle, with bushings in the side rods as on the 773.  Lionel and Flyer grew up during the Machine Age. They knew better, but both took the easy way out!  Good luck with your trouble-shooting, please let us know what you find.