Again I ask:
Do I see an o-ring on the transmitter fitting? Should it be there when using a hose?
If replacing the seals don't work, try a different type of spool. There are a few different types of spools-you may just have to find the correct one.
I just found the following video by Suunto on youtube.com that shows the transmitter being mounted on a HP hose, o-ring on the threaded fitting included:
My guess is it should be remain there but I will test without submerging to see if it seals. It fcould be that Suunto mucked up when they made the video.
My plan is to take the transmitter to the dive shop when I go back later this week after they have a chance to test the hose I dropped off this evening...this way different spools can be test fit.
-Z