Ongoing saga for me as car is a weekend hobby and doesnt usually come out of the garage if its raining. Anyway noticed foam under passenger carpet was really wet after I purchased it. Tried all the usual like door membrane, clearing drain holes, scuttle by windscreen and any leaks around door seal end of last summer. Couldnt find a thing wrong so dried everything out and hoping it was a legacy issue which had previously been sorted made the mistake of going to Newlands Corner last Sunday in the rain and more rain and ponding issues on the road. Checked behind the passenger seat where there is an overlap join in the carpet and sure enough the underlay foam is wet.
Cannot think where next to check and a bit worried that rust could set in on the floorpan, although no sign of it when I dried it out.
I did read on here that even though the roof motor drain hole can appear unblocked it is difficult to clear completely, so probably now left with deciding whether to remove rag top or just live with it and dry out carpets every few months.