Update times!
Superglue did bugger all (yeah yeah, you told me so! ) so I had proper play with it this morning. I poured a crap load of water right into the hole and it ran straight out down the bottom, just like it's supposed to. This was after I'd fiddled with the central part of the seal, so I think that's where my problem lies: Not sitting in properly. If that's the case, then it's not really an issue at all and I can live with it (especially since it now seems to be fixed).
Out of curiosity I had a look at the one on the pax side, and it turns out it's got the exact same tear in it, so I wonder if it's by design? Would any fellow roadster owners like to do me a favour and go and check theirs if they get a chance please?