So, when I first got this new car I didn't go with the dealers autoglym whatever deal. Instead I took it to Jonny at Pure Detail.
He left me clear instructions which I passed on to the dealer, not to touch the car body work. So, when I picked it up it was still covered in the plastic and delivery stickers, as well as a load of dust and muck.
Anyway, at his place he told me he had a waterproofing bit of kit that we were going to try on the roof as part of the detail. Its been on now for 4 months and is still exactly the same. In fact, I was at the dealers just yesterday and the sale guy commented on how brand new the roof was looking. Because, essentially, it is. Nothing has got thru to lay on it. This was the video we did after it was first done and really I should get another at 6 months and again in a year.
The product is from GTechniq which seems to have been borne from the sailing world but it works an absolute treat. Water is like mercury when it hits it and if you have a new soft top, I cant recommend I1 Smart Fabric enough. As Jonny at Pure Detail will tell you tho... it doesn't make you yourself more waterproof! ;)