Hi Calan.
Leeroy may be partly right as a stuck crankcase head will also make them stubborn to remove. If it has seen salt, the tighter it will be so I do use a crowbar type tool to carefully pry around the edges of the block to crack it loose. The secret is to go around evenly and not pry too hard. Back and forth, back and forth. Once it breaks free, it will lift off quite easily.When putting it all back together, I like to coat the head with Triple Guard grease to make the job easier the next time it has to come apart.
Here’s a 9.9/15 which had this problem. The shiny area is where the corrosion happens.
The head is #11 in this diagram.
