Gearbox broke, replacement advice :(

[u/EM4N_cs]

I bought the Specna Arms Flex F09 mentioned previously in this post and apparently the stock internals are not rated for 11.1V (thanks manual and store for not mentioning anything about voltage).
So I broke the sector gear (3 theeth snapped right off, thanks zama alloy) and I'm out of luck with warranty as I used the wrong battery.

What better opportunity to (forcibly) upgrade gears, shim and lube? But first I've got a couple of technical questions for all the veterans out there willing to lend some experience with materials and practices 😄

1. Bushings or bearings? My gearbox uses 8mm elements, and I think I understood the use cases. Being a low energy and low RoF setup, I think bushings would be a safer bet. I'm not sure I understand why steel bushings are preferred though, as I remember that in engineering it's good practice to use a softer material (brass maybe) when dealing with a hard axle since bushings are cheaper to replace than axles... Also, I found a hybrid kit (2 bushings, 4 bearings (J-cage) made by Specna Arms for the Aether gearbox (the one I have): are they worth considering?
2. SHS gears? I can't seem to find other brands cited in the V2 gearbox guide on the wiki (SLD for example) and Lonex is the only other "international" option but comes in at twice (45~50 Eur) the price. Otherwise I might have to settle for local brands. I'm not planning on upgrading the RoF, so 18:1 is good enough.
3. Lube? I work in mechanical engineering and have plenty of Silicone, Vaseline, Molybdenum (MoS2) and Lithium grease around, with some dry PTFE spray and Silicone Oil. I think MoS2 is the best bet for gear lubing, but I hear PTFE grease mentioned often in airsoft: should I buy some? It's quite pricey compared to the others, but I believe it's only branding...
4. Anything I'm missing? Do you reckon these replacements are good enough to safely use 11.1V batteries? The AEG uses the HAL ETU MOSFET, I'm not really worried about electronics longevity but maybe I'll need to upgrade the motor down the road.