tie downs on swim platform 2006 Sovran 3600

[sluggo]

there are so D ring type tie downs on the swim platform .  I think one is 'leaking', that is water is getting in the screw holes.  I went to take them out, and rebed them with some 4200 (decided against 5200 seem to permeant to me)  Anyway, when I backed one it appears to be a bolt and not a screw.  I don't see where these are through bolted, so I wonder what keeps the bolts tight in the hole. (can you say that on here?)  Are they just 4200/5200 in the hole and that's it?  or is there some sort of nut or thing (tapping) in the hole to that keeps them secure?
Any thoughts or ideas on this matter is appreciated.  I don't like the water getting in the swim platform and 'rotting' it out.  
tia