I don't think the channel has been replaced/repaired although I will look a bit harder. I haven't seen any evidence of any previous welding at all on the car, save for one door hinge mounting on the door, and that looks to have been done very nicely, the only other repairs I have seen are a couple of bits of brazing on the bottom of the headlight bowl, and a little on the front valence which you will see on earlier pictures after I stripped the paint, so as far as I can see the car is untouched in that respect.
I too have read about using OEM seals, and this is something I plan to do. I am a bit unsure at the moment where to buy parts from, I spoke to the local MB agent and they can get me quite a bit, it's just knowing what to get, for example I will need a new tail light panel, do I get this from MB or aftermarket, I suspect that the part supplied by MB may well be the same part as the aftermarket suppliers? Or do Mercedes actually make these panels?
Certainly in the Corvette world there is a huge disparity in quality from one manufacturer to the other, we wont touch Ecklers parts for example. I'm hoping that these very expensive parts will fit a lot better than the repro stuff I am used to. The Mustang parts were even worse, I had to replace the doors on my fastback and they were completely different sid eto side. I spent weeks adding metal to the door edges to make the gaps come right. That's one blessing with the Mercedes, the gaps are all very nice to start with and none of those panels need replacing.
I will have the sandblaster go over all of the areas I haven't stripped so he will do that channel, the soft top bin, floors inside and out, windscreen frame etc etc so if there is any rust lurking in those areas it will show itself.
It is also good advice to prefit everything before the car goes to the painter, I do that as a matter of course on all the cars we work on to save any heartache after the car is painted.