Acryl is a thick liquid, silver colored which you can apply with a hand pump and good nozzle for careful application to the seams
There is a product called Dr. Tolleys which is great. It wicks into the tiniest seam/crack
Now, there is a thread here for a compilation of products useful for this perpetual maintenance.
Sounds like you need to drop the belly pan... It is almost guaranteed there are issues in there which can harm you. It is recommend (do not take this lightly) that proper respiratory, eye and clothing be used for protection. You may/will find remnants of mice, etc...which are bad for us humans...
If I can find the sealant thread I will post here...
Got it..
http://www.airforums.com/forums/f456...ry-116214.html