My Merc has the shift built into the handle. It shifts into and out of forward gear just fine but I've been having trouble shifting into reverse. If I can get it in reverse, it's fairly smooth and sometimes very smooth and it comes out of gear just fine. Otherwise, I can't get into reverse at all. My fiance's father who is a Merc mechanic said it's probably a linkage issue. Any theories? If it is a linkage issue, how do I fix this? Please be detailed as I'm new at this.