A couple of the bolts in my deck-hull joint have started leaking after 40+ years. Luckily cleaning and rebedding them is very easy! I use simple ethanol to dissolve the old butyl tape and rebed using new butyl tape. Good for another 40 years 😉
Blog post about how to use butyl tape: http://www.pbase.com/mainecruising/rebedding_hardware
I purchased butyl tape at this place: http://www.pbase.com/mainecruising/butyl_tape