Need some help problem solving wiper issue.

Background: When I got the 67 Bird the fuse was removed from the wiper circuit. I replaced the fuse; wipers didn't work and motor got very hot. Took it all apart and started troubleshooting. Disconnected linkage arms, checked all wiring, fixed a weak ground issue. Switch is new. Motor tests out fine in low, high and park function (linkage disconnected). Hooked it all back up and motor moves 1/4 turn and then locks up.

Ok, problem must be the linkage. Wiper arm pivots were a little crusty and didn't turn freely, must be the issue. Took linkage completely apart, all copper ball sockets were in good shape, so I just cleaned, lubed and reassembled. I couldn't figure out how to disassemble the wiper arm pivots, so I soaked them in penetrating oil overnight and after a ton of lubrication and cleaning they move pretty well, with slight resistance. Put linkage assembly back in the car and can manually cycle the wipers with minimal effort, everything moves smoothly.

Hook the linkage back up to the motor and it again moves about a 1/4 of a turn and then binds up. I can 'help' it rotate to about 180 deg and then it locks solid. I cannot physically see anything binding.

I'm at wits end. Is it possible that even though the motor operates correctly under no load, that it is faulty and doesn't have enough torque to overcome the linkage resistance? This is the only logical explanation I can come up with but haven't seen this condition before. I don't want to start spending $ buying parts without knowing the culprit.

I've heard the aftermarket linkages aren't very good and mine restored nicely, so not sure that will fix the problem. I know there are lots of improved aftermarket motor solutions, but they are pricey and my wipers will never be used. I just want everything to work. Should I buy a replacement stock motor?

Any suggestions?