After checking around, there's much that can be used to remove
silicone  sealant if it's uncured, but once it's cured, nothing short
of commercial  solvents will be able to dissolve it. On a fish tank
messageboard, one user  describes how he takes apart old tanks sealed
with silicone sealant (linked  below):

"Commercially lye dissolved in tetra hydro furan is used to  remove
cured silicon
rubber. this is extremely nasty  stuff..."

General Electric's Sealants & Adhesives website has  information on
removing cured and uncured silicone and says it is VERY hard  to
remove. They give step by step instructions for removing  silicone
sealant on different types of surfaces such as wood, tile,  etc.
(linked below) The recommend using mineral spirits and rubbing  alcohol
which are less abrasive than the stuff used by the guys above,  but
will probably take longer to dissolve. GE's step-by-steps rely on  a
little bit of elbow grease to speed up the process.


Additional  Links:

Silicone sealant removal thread:
_http://www.thekrib.com/TankHardware/glass.html#10_ 
(http://www.thekrib.com/TankHardware/glass.html#10) 


Search  Strategy:

"dissolve silicone" sealant on google:
_http://www.google.com/search?q=%22dissolve+silicone%22+sealant_ 
(http://www.google.com/search?q="dissolve+silicone"+sealant)