I have a shower which has a join between glass and marble which has recently started leaking. As a first step, I've removed the grout for replacement, but it looks like there's some sort of rubber seal underneath, which I believe I need to replace as well as it's located where the leak is coming from. What is this part called, and is it part of the waterproofing mechanism? Is this the only thing I'm likely to need to replace in addition to putting new grout and sealer on?
It appears to be a silicone/butyl rubber seal, that will prevent moisture intrusion and also allow for the expansion and contraction of the two different materials at that joint. Each material has different expansion and contraction qualities and that silicone/butyl rubber seal is providing the space needed to allow those materials to do what is necessary. So it is in place for more than one purpose.