I think the issue with the 1165xx's with mod 7750's is more of an issue on WHEN they will fail, not a question of if. The extra gears and wheels add a lot of resistance to the original gear train... Imagine a Toyota Corolla motor in a Yukon Denali body, pulling another car up a mountain pass with 7 passengers inside. That would be the equivalent in my perspective. The problem is likely with any movement- New Asian 7750, old 7750 B1, Swiss 7750, etc. And since parts are not exactly easy to get for this bastardized movement, the issue of repair becomes a problem if new parts are needed, especially if it's to replace one of the added parts to shift subdial output.
Having owned a number of these models myself in the past, I've had more problems than success with these movements. To date... I own none, and it will most likely remain that way. The only way I'll own a 116520 is if I ever decide to buy the gen, or if I'm able to get my hands on a genuine 4130 to build another frankenstein like the El Primero.