904 leak...dipstick???

The trans moving because of the mount wont make it leak because the dipstick tube is bolted to the bellhousing.
Usually leaking while sitting is either the dipstick tube oring as mentioned, or the linkage seals where the shift lingage goes through the trans case. (if the leak is at the front of the trans)
The dipstick is on the passenger side, and the linkage on the drivers side.
Be sure and grease that oring when you put it back in so it doen not tear or roll the new one.