possible leak from speedometer?

so far this year we have hit a lot of debris in the sacramento river, we have had to replace our prop twice. on that note I've recently notice that our bilge has been switching on automatically a lot lately, and at this point it will not turn off. I was wonder how exactly the speedometer measures speed/temp etc. as I think this opening may be leaking into the boat. thanks, Trevor.

it will leak onto the drivers feet or lap if its speedos, i would guess your packing is leaking at your shaft...i am assuming you are an inboard or v drive. so you just need to tighten the packing nut/ or replace the packing(waxed rope) these will leak more and more and need to be snugged up to keep the leaking to a minimum. if you've never replaced the packing its pretty easy, if its old all the wax is cooked out and it wont seal anymore...its under $10 for the new packing.