Here goes my attempt at showing you my fix for a convertible roof which leaks at the corners. Could possibly work if your roof leaks in other areas along the front seal.
When I bought my car in the summer, I didn't worry too much when I got a wet leg every time it rained, I just put a bit of kitchen roll in the gap and made do.
I researched this forum and saw other convertible owners suffered much the same thing. Reading up on the internet I watched people using silicone on their cars, so I too tried using silicone on the front seal to no avail.
Seeing as it costs hundreds of pounds for a replacement at BMW (even then it's not guaranteed to keep the water out) I decided to see if I could fix the leak myself.
My apologies for the noddy guide, but I'm an engineer and understand some people need war & peace for the simplest of tasks
Firstly, have a look at the seal, and see where it has aged/cracked/perished, as it is through this part where the water is getting in. In my case the corners.
I had a look online for a small adhesive backed rubber seal which would fit comfortably where the roof comes into contact with the top of the windscreen. Without being so big as to cause more problems than it solved!
I got a 1m length of seal from this website:
http://www.sealsdirect.co.uk/index.asp item no.SRS1706
(cost me about a fiver - 3.99 of which was postage!)
On a dry day (which is the most difficult part of this job with the recent change of weather!) open your roof and clean off any grease, dirt etc from the top of the windscreen - where the roof comes into contact.
This will help the seal to stick.
Once the windscreen is clean, cut your seal to the required length.
(Picture 1 shows how long I cut my seal & where it's positioned. It's flattened a lot near the corners since fitting)
Stick the seal down with the flat part of the seal to the front. (Picture 2)
Once you have made sure both sides are stuck down securely, close your roof (hope for the best) and leave to set. Leave for a day or 2 before/if you need to open the roof.
Now, hopefully, your leg will stay dry and you can stop robbing the kitchen roll!
Picture 3 shows just how wet it has been this week and I haven't had a drop of water get in - other than the ones I had taking the pictures for you!
Hope this helps, as you can see, if it works, it's a cheap fix, even cheaper if it wasn't for postage! Let me know how you get on.