Eliminate the easy culprits first. Side trims may be the reason so spread a bit of weatherproofing goo around the clips. I replaced all my wire clips with a plastic sleeve with a small bolt and nut that slips into the trims and screws onto the side panels (absolutely waterproof). I can't comment on the possibility of it leaking through the rear screen as I have just replaced mine with a new seal (old one was hard and perished). The boot seal is an ongoing problem with my beast. I have seen other 120s that have only had the bottom part glued and the top loose to enable leaves and dirt to be easily cleaned out and no problems. Personally I like to glue the whole thing down. I have had several attempts at this and have used the black rubberised 3M product after being recommneded by professional car restorers. I am not totally convinced on this as mine has still pulled away from the top area. This may be because of a pressure problem with the trunk lid adjustment as when I close the trunk the seal wants to peal away which it has done on several occasions. I have just imported a tube of Bostik 292 from Sweden which is supposed to be the rcommended glue to do the job. I am now onto my 4th attempt. One hell of a job as cleaning the stuff off is as messy as getting it on there in the first place. Another option is the yellow 3M weatherproofing glue which I have not tried. It also may require you to remove the trunk lid to get decent access around the hinges. Best of luck.

Bilo