My/the manual does say 100hrs or 1 year - whichever is the soonest.
........... though I have greased all the grease points twice during the "season"....... except for the fact that I still can't get grease down to the lower bearing on the pivot shaft !!
I have also followed the rules of opening the cowl, saying nice things ......... like WOW ....
My local merc man does suggest that at 50hrs you - change the gear oil for synthetic, drop the box to check the impellor and grease the gearbox mounting bolts - since they are dry assembled and it can be fun trying to seperate when you do need to change the impellor later ?
I have opted !!!
for this - even though I have done 60 hrs before I could get round to it.