Oooh I do like the rubber coated ones ....sorta self sealing and fitting in the bore and thusly bore interference isnt critical . I have used the non coated ones and yes the bore fit is important with them but then the also need some sort of sealing compound on them to insure they dont leak around the outer circumference of the seal . Im thinkin too that the non coated ones I have sourced/used have all been nos parts on older stuff . I think rubber ones are ok I mean its not like the seal is load bearing , all they have to do is stay in place and anything with a bit of pressure behind it usually has some mechanical retention involved.
