Regarding the fill port: I've done them just to preserve my sanity.
I borrowed my wife's ex's Escort for a trip, didn't really know what I was doing, thought I'd help out by changing the fluid in the 5-speed. Drained the fluid, then discovered that I couldn't remove that speed sensor. Ended up paying the ex for a tow to have the dealer remove it.
Four years later, I won the car, now it needs a clutch. got it done, take it out, clutch is good, but randomly I'm locked out of various gears. In reinstalling that speedo gear, I thought I was running into opposition from the sealing o-ring because the plug is such a snug fit. Wrong. The two gears weren't meshed properly, I forced it, and the gear ended up at the bottom of the case, where it was blocking the shift mechanism. Pulled the transaxle, opened the transaxle, retrieved the gear & clip (undamaged), reassembled the transaxle, reinstalled the transaxle, drank heavily.
Another few years, another Escort, another clutch, fill the transaxle, reinstall the speedo thing, car runs great, but no speedo action. I'm not sure exactly what it is (for this one I used some heat shrink tubing to ensure that the clip stays put). I no longer CARE. I don't need a friggin' speedo! I just need to NOT go back in there again. here are photos of my fill/check port, this allows me to drop a dipstick straight down past the inside of the "elbow" of the air inlet. I've seen several times that it'll leave a puddle of ATF at startup, and it's pooling on the top, so I guess I overfilled it, and it's leaving via the vent. This motor/trans was used in the SpecRacer Ford series, and there's some suggestion for purposely leaving the level low, so it doesn't drain out and make a mess
when you pull if you change the axles. Sounds crazy.