403 Windscreen outer seal
 

I've just rebuilt my 403 windscreen. I'm now struggling to get the main outer seal installed. I've tried sliding it in before bolting the two frames together but after a few inches it gets too stiff. Is there some knack or tool to use to push it into the groove in the frame edge rather than sliding it round?

outer rubber insertion
 

Sliding it in is not a workable option as you found and as I found recently. I have a plastic insertion tool which is really just a wide screwdriver like end which is curved.
I inserted a length of the front face of the seal then used the tool to prise in the rear part. I only did this in small sections - about 60 mm at a time and used glycerin sparingly as a lubricant only on the rear facing part of the seal.
The corners - especially the tighter ones take a lot of patience but it does go in. A few swear words here and there seemed to help.

That's both helpful and encouraging - thanks. Not sure where to look for the plastic insertion tool you describe - perhaps you could advise. Is it the type sold for opening up phone and tablet cases? Or something larger?

Windscreen rubber
 

Washing up liquid is also a good lubricant and any small blunt tool will help - eg handle of old spoon etc. The seal I got years ago from Bristol Cars was alas too big and it took me a long time to realise it would never fit so make sure it looks ok. (In worst case , if all else fails activate Plan B and take it down to a windscreen centre-shhhh!)

Job done! Thanks to info from both responses I have just finished installing the seal with the help of a blunt screwdriver. The rubber was robust enough to withstand the treatment. I joined the two ends together with a bicycle inner tube repair patch and then filled the join off on the outside with black polyurethane sealant. I have not bothered with the staple that the service manual mentions. I'll see if that's necessary when the windscreen assembly is offered up to the 403 when it comes back from the paintshop.

401 windscreen seal
 

Can anyone suggest where I can either find the correct outer rubber profile for a 401 windscreen or alternatively provide a picture of the correct profile?

I got mine from BODA.