Just wanted to provide an update to this post. I found it helpful, as I recently had this same issue and needed to replace the motor for my hydraulic pop-out on my trailer. The links provided originally got me in the right direction, but Ultimately I was unable to purchase the item from those vendors. If you are still looking for this part, check out Amazon.com, and I purchased it here: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
I hope this is helpful to someone else as it was to me.
The Part # to search on the web for is: ARRTRM0008 or try searching for "Trim Motor For Mercury and Mariner 3 WirePIC 107-122M3 WireReplaces Mercury 17649A1 and 87828 MFG# ARRTRM0008"
Thanks and Good Luck!