I've done plenty of fluid changes on the manuals in my cobras. I have 3800 miles on my car and it's been getting harder to get in 3rd and it's really "notchy" for lack of a better term driving around now. I did change the fluid once before and didn't pay any mind to it. I just put it on the lift....and when I opened the drain plug ....wwwooooshhhhhhh. Air rushed in and fluid drains really slowly out of it. I cracked the top fill plug and of course it drains normally. What could cause this to pressurize like this. I'm pretty sure there is a vent to prevent such things. Where is the vent located. I can't remember where when I had it out to do the clutch. Could this cause some of the hard shifting issues.