I have an 09 GL1800 and have not had any water problems with the trunk. Some questions I would have are
is the seal around the lid broken or crimped by something which would allow water in?
do you have a wing or trunk rack installed? check for leaks there.
is there a crack anywhere in the trunk lid or body that could cause water to get in?
do you have side lights or after market moldings or stock moldings that may be loose?
The Wing is pretty water tight so its unusual to have a water problem. Hope you find the source. before anything else gets ruined.
is the seal around the lid broken or crimped by something which would allow water in?
do you have a wing or trunk rack installed? check for leaks there.
is there a crack anywhere in the trunk lid or body that could cause water to get in?
do you have side lights or after market moldings or stock moldings that may be loose?
The Wing is pretty water tight so its unusual to have a water problem. Hope you find the source. before anything else gets ruined.