See if it runs smoothly, as Larry noted, that's where I'd start; and, then go from there. There are some lubricants, or it may be the lead of the cable to the engine got distorted by someone, in any event, the cable motion shouldn't be loose, but it should be smooth. Now, with the boat carefully secured with forward and aft spring lines (and the rest of the restraint package at dock) try to manually move the transmission into forward, reverse, and neutral. See if it seems to be working properly. Again, it won't be "loose" -- but it should be smooth when it goes in and out of gear.

I don't understand the issue of the creep on the forward/neutral/reverse on the Yanmar being related.