I have the Jet version of this lathe and it had the same problem. The casting for the lock was horrendous, and it would always bind. It wasn't flat and it didn't match the underside profile. Still, I found that much of my problem was paint on the sides and underside, but there were some rough spots that I took care of with a file in an improvised jig.
The original lock would bind due to the offset that you describe, and a spring didn't cut it. I machined a much larger, heaver one that kept it guided so it would not rotate and bind, and machined the steps to match the offset. The bottom of the tailstock also was far from flat or matching the vee, but I brought it in by filing and scraping. Now I can adjust it to <90 degree turn of the nut to lock it, and it never slides when locked.
Vast improvement in enjoyment operating this lathe.
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