After loosening the vent's cap, the oil drip persisted. I was planning to change the trans oil so I decided to wait till then to look at it again.
Ordered the Redline MT-90 as widely suggested in this forum, had to cross the border and go to Michigan as I could not find it in Ontario.
Opened the fill plug first and guess what.... heard the "hiss" again.... the transmission was again under pressure. Completed my oil change and then decided to remove the battery and tray and see if I could remove the vent and clean it thoroughly.
Didn't know if it was press fitted or threaded. Space is tight so I took a very small vice grip, grabbed it by the base and started turning it counterclockwise. I was glad to see it turning. After numerous turns it came out, the thing is press fitted.
(see how much cleaner my transmission is now hate having a dirty engine)
Once off, I tried to blow air through it, it was completely plugged (or seized). I placed it in hot water & soap for a while and then tried to clean it with a toothpick. There was a rubbery/springy thing inside it which made me think and later confirmed this vent is more of a one way pressure relief valve than a vent. This is new to me, the one I found on my Sienna's rear differential was just a fitting with a lose cap on it.
Once cleaned and unplugged, I started throwing WD-40 at it. Got air to go through it with a bit of effort so again, it behaves like a pressure relief valve.
Putting it back required some imagination, is pressure fitted and the starter is on top of it. Used a bar and applied pressure leveling against the starter, then I gently tapped it down using a hammer and screwdriver on the edge of the base.
I'm not 100% satisfied with this as I do not know if the valve is opening at the pressure it is supposed to and I do not know if the cleaning process and years of grime might have altered this. On my next opportunity I'll stop by the dealer and order a new one, so far I haven't been able to find the PN but it cannot be that expensive.
Here are my thoughts about this:
- If you have an oil leak coming from one of the seals, replace this valve. Its a quick DIY that might solve the issue.
- I wouldn't waste time cleaning it, as I said, you'll never know if its working as intended.