This subject pops up quite often whenever the MGA leaks rain water under the front edge of the convertible top and drips off the windscreen onto your knees. When I drive daily in all kinds of weather, it is bound to happen. It may be more serious for some people, as rag top installation is not always done in the best form. I have played with various seals over the years. One of the slickest tricks is to embed a strip of foam rubber underneath the front wood bow before it gets the fabric wrap. The rubber strip is then weather protected, and pretty much invisible, and it may work okay for most people. Be sure the rubber is very soft, because you have to crush a strip nearly 4-feet long by pressing down by hand.

I find that in most cases people have not planned that far ahead and need to find a seal solution after the rag top is already fully installed and in service. This is I think the best seal I have found so far. I bought this one at Home Hardware in Nova Scotia, Canada in late 2018. It is Weather Shield brand, part number 2395-367. Never got around to installing it, but now that someone brought it up again, maybe very soon.

It is very soft foam rubber with sealed outer surface. The Double-D can be easily cut to make narrower Single-D strip. The "D" shape is 5/16" wide x 5/16" tall with a small space in between, the whole strip being 3/4" wide. Peel the wax paper off and stick the rubber seal to the under side of the front bow, then just attach the top to the windscreen in normal manner, and no one will ever see it.

If the gap is a bit much, and it doesn't seal completely, you can stick a second strip on top of the windscreen frame, offset to interlock as shown. This gives multiple contact points and a labyrinth path that will likely be impermeable. Center photo shows my cell phone sitting on it to hold it in place for the picture. Third picture has one finger on the cell phone to show how easy it is to crush this stuff, and how snug the resulting seal is likely to be. When I do get it installed I will post more pictures.

Before I installed a new top in early 2018, I had a similar seal installed here. That one was not foam rubber, but was thin soft vinyl in Double-D form, about the same size. The "D"s were a bit farther apart so when overlapping one "D" would nest nicely between the others without being deformed, and it didn't add any significant thickness. That seal was removed when I installed new windscreen glass in early 2016 (and again in early 2018).