Rear window sealing - At my wits end.. any ideas????

[79300D]

Okay, this is not the first one I have done, so, I am pretty familiar with the process of replacing the rear window seal on the W123 body. This last car REFUSES to seal correctly along the window bottom. I have had this in and out 4 times now, and it is STILL leaking around the bottom of the window. The water is going in on the front of the seal, under the window, and then up on the interior side of the window. I have tried everything. It is very well cleaned, fitted properly. I assembled the WHOLE unit including trim before putting it back in. I should not have to apply any sealant to the seal before installation should I? I never have had to before. The seal is an OEM and has no noticable flaws.... any ideas?

Cheers

Jeffrey