Mechanic Question for 2005 Mercury 175

I just had my impeller replaced from the shop. I towed my boat home and parked it. The next morning I noticed green (gear oil?) leaking from a 'weep hole'. The hole is on the starboard side, just below the cavitation plate, and about 1/8" diameter. I called the shop and sent them a pic of what I was seeing, they said it is most likely a shift shaft seal. I never took my boat out, went straight from the shop to my house. My engine did not leak prior to taking it to the shop.

My question....Having the impeller changed/worked on, could the shift seal be damaged? What I am getting at, is that there was no leak prior, and just want to see if the shop is responsible for the leak or is it just the cost of being a glorious boat owner. Just don't want to get taking for my $.

I am trying to upload a pic of the 'weep hole' where it is leaking from.

Thank you in advanced!Attachment 50642