Rub rail sealing help

[Captain TJ]

I have a pretty significant leak into the cabin from the rub rail area. I have already removed it all but about 5' which I will remove and clean up to seal after I put the other end back on. Wanted to keep part attached to keep the same orientation as before. Once removed it became very evident why it's been leaking. Also evident that someone has tried to seal it previously. I plan on sealing the gap between the upper and lower form with 5200 and all holes and screws with 4200. My big question is the plastic terminal ends of the rub rails at the transom are cracked and I would like to replace them as well as the white plastic pieces that cover the joint between the engine mount of transom and the sides of the engine well. I have not been able to find these for sale online anywhere. Any help locating them would be appreciated,

Thanks in advance