Speed & Depth instruments leaking water

[Kefalonia]

Hi,

The seals around my depth sounder and speed/distance instruments seems to be failing. They are leaking water at an at-present not too alarming rate. The problem seems to be that whoever fitted them has used silicone instead of sikaflex and the prolonged submersion has worn it. A couple of questions - do you think this will get worse or will it last until the end of the season if managed?
Secondly, if I want to reseal it without taking the boat out of the water is there a way of resealing it? I've heard of a product that can be used in the water to seal from below, though the guy didn't know what this was. Any ideas?
Thanks in advance