I have done this job on my 36(!) year-old boat. I too, had grey goop in various stages of gooey-cracked-n-dry-leaking condition. My first step was to have the toerail powdercoated before rebedding. It really made a difference in the look. I used a polysulphide bedding compound - lifecalk - at the recommendation of a reputable yard. So far so good. The only issue i've found was mine - I moved to quickly to tighten down the toerail before letting the lifecalk set up, and squished too much of it out. Fortunately this was in just one or two spots on the 36 foot run of the rail. 6 years later things are water tight and look great. The calk is still pliable and working and the powder coating looks great except where heavy abrading had worn it down to metal. Still, looks a helluva lot better than the corroding, chalky white pitting that was there prior.