The bow thruster shear pin replacement was the only Thruster repair that I, as a DWT-DIYer (where DWT = Don't Want to) was able to easily complete while the boat is in the water. Remove a few bolts and you see a shredded mess of the old pin and replace with the pin that, in my case, came with unit as a spare...then, order a new spare. If you determine a leak, the repair cost will be considerabley less.
I'm going to make a separate post about my Stern Thruster and the awful support that I've gotten from Lewmar, both US and UK offices. The short version is don't trust them, they provide false information.