I have a slight leak to the interior along an interior corner edge of my Dorade box. I dug out the old caulking and have been planning to reseal with Sikaflex, but it will be a messy job as the work has to be done thru the 4.5" diameter cowel hole. Butyl would be a lot cleaner to work with, but will it make a good seal as an open fillet? The corners are somewhat concave, ie less than 90 degrees, giving somewhat more surface to adhere to than a 90 degree corner would be.

If Butyl is not suitable I'll probably use a caulk that is available in a small tube that would reach inside the Dorade, unlike a cartridge. Sikaflex 291 comes in a small 10 ml tube but after searching the web only the larger cartridges seem to be available here in the US.