Well then, since that's settled, here's the summary of the effective job completed on my VFC Avalon MK18 as I understand it (not in any particular order):
Problem: Broken spur gear tooth
Solution: Replace with SHS 16:1 (stock ratio) CNC steel gears, and shim
Observations: This gear broke VERY soon in the gun's life, perhaps a lemon. I accidentally messed with motor height before I knew what I was doing. The top of bevel gear was scraping on the inside of the GB shell at some point. No other evidence to suggest fatal motor height issue.
Problem: Trigger locking up on semi-auto, feels as if on safe. This problem was present since brand new OOTB. Eventually progressed to firing full-auto in semi.
Solution: New, higher quality trigger switch assembly. Unknown brand. Black in color, unknown material, good quality casting/machining. Labeled SHS from my local shop, but I've only seen red V2 units from SHS and they look of lower quality than this one. To maintain the original VFC MOSFET, I de-soldered everything from it, unscrewed the plate holding the trigger contacts in the unit, then carefully separated the MOSFET from the contact assembly with a small flathead screwdriver. Once removed, I VERY CAREFULLY sanded off the old, dried superglue*, placed the trigger contact unit in the gearbox, and got an idea of how I wanted the MOSFET to sit. I put the small body pin in place that would normally be there once the gun is fully assembled. I then proceeded to apply super glue quite sparingly, spreading it around the contact assembly surface without getting too close to the edges in order to avoid squeezing it out into places I didn't want the glue, then pressed the MOSFET into place and held it there with good, even force for about 2 minutes. Re-soldered it back together. Good as new.
Observations: It would be a very good idea to take pictures of anything wiring related to be sure you put everything back the way it should go.
*Be VERY careful when doing this, as you may sand away silicon and expose the leads in the PCB. Not good. If you mess this up, you could still cover it with super glue, but you may have added some resistance to the circuit if you removed any of the electrical lead.
Here's a secondary part of the job that was due to my own errors and/or having used a different gearbox shell:
Problem: Broken screw stuck inside VFC "ECS" Gearbox shell
Solution: Replaced with Lonex Gearbox shell -- 8mm ball bearings and proprietary tappet plate included. Failed to extract screw from VFC shell.
Observations: VFC cylinder has a tough time fitting in the Lonex shell, as does the trigger contact unit. You really have to muscle these pieces in there for them to work. I do not recommend using these trigger contacts in this scenario. I suspect if I went with another VFC gearbox, there would have been significantly less headache with this job. VFC seems to like not doing things to Tokyo Marui spec, or perhaps their tolerances/QC are ****, or my particular unit just happened to get the **** end of the tolerances on a bunch of parts. It's truly a mystery to me. I wish I had just gotten a complete Lonex gearbox, or a VFC ECS shell.
Problem: Low FPS (~150 FPS on Lonex SP100 spring with either .2g or .28g BBs -- got mixed up in testing) -- nozzle not moving during test fire, unable to be pushed back or pulled forward.
Solution: Used a Dremel to cut down the sides of the tappet until it had enough space to move the way it should. I ended up removing about 1mm on each side, nearly flush with the recessed portion of the tappet plate that Lonex cuts out in order to fit around the extra reinforcing material inside their gearboxes.
Observations: Very strange to me that this tappet plate did not glide freely in the gearbox it was designed to work in. In fact, it didn't move at all when assembled, it would get pulled back by the sector gear, then stay seized in place by the gearbox.
Problem: Feeding issue
Observations: Initially, it was feeding ~8/10 shots at the beginning of my latest game day (Sunday, June 28), by the end it only fed ~1/2, sometimes double feeding.