On rear windshield rubber, if you mean the exposed external molding, you will need to replace the whole glass with one either from a junk yard or have a new aftermarket glass put in (comes with the molding attached). There's nothing I know of that you could cut the old molding loose from the glass and glue in place of it that's not going to "look like ass" as the kids say these days. When I painted my Concorde, that molding was in bad shape, and I cut a complete rear windshield out of a junker and had a top-notch local glass company R&R it. The cost for the R&R was $120. It looks great - looks just like it did from the factory because I selected one that was perfect from the junk yard and the installer did a perfect job. It was a pain cutting it out of the junker (you have to be careful not to damage the defogger grid and antenna connections if your car uses the grid as the antenna) - probably would have been no big deal for someone with the proper tool and skills who does auto glass R&R for a living.
Going the new glass route could be pricey - our rear windows used to cost in the $600 to $700 range just for the part even in aftermarket - that's why I went the junk yard route. Maybe the price has come down over the years - you'd have to check on that with a local glass company.
On the front windshield, you must either be talking about the black adhesive between the glass and the car body *or* the painted molding strips on the left and right A pillars and their black coating is peeling. I doubt if you mean the sealer, which leaves the 2 side molding pieces.
I replaced those moldings on both my Concordes with new parts from the dealer years ago when they started peeling, and the replacements were much better for their coating not coming off - they both still look brand new after many years. If they aren't available anymore (check eBay for new-old stock using the Chrysler part numbers -delete any leading zero, if any, from the part number), you could remove yours and peel all the stuff of and either leave them bare metal (they don't rust), or paint them - maybe spray Plasti-Dip them - if you want them black, which I would prefer.
Ronbo is right about the cost to restore everything. You'll blow right thru the blue book, and then some. Nothing wrong with that as long as you do it with eyes wide open. If you rebuild the front suspension and take care of everything else with TLC, it could almost be like driving a new car. I did it with my '98, and then lost the 3.2 engine a year later (timing belt broke) - so for that one, I transplanted the 2.7 from my '99 with damaged body into it and scrapped the '99 body and '98 3.2 engine, and it's doing fine as my daily driver. My signature photo is the '98 after the restoration.
If you decide to take the plunge to restore it to a reliable and aesthetically good car, check the brake lines and metal power steering lines in the engine compartment along the driver's side fender and the rear brake lines on the driver's side just ahead of the rear wheel for heavy pitted corrosion. If they are, put those on your list of things to replace. If they are heavily pitted, they *will* eventually leak, and the break lines *will* rupture if you have to make a hard stop. Happened to me in my '99 about the same time as the engine went in the '98. Fortunately, when the brake line ruptured during a panic stop, the driver in front of me saw my dilemma and moved forward to give me room to stop with brakes on only two wheels working - a nice little adrenaline rush there! Also, for some reason, the power steering and brake lines only had minor surface corrosion on them, making my decision on what to do with the two cars easy. But my point there is to not ignore those lines. If they are heavily corroded, they can't be ignored - they are a real safety hazard.
So yeah - go for it being aware of what it's going to take time- and money-wise, and even then, there's going to be risk of additional issues after your done (like losing an engine or transmission or whatever). And you'll never come close to recovering the cost by selling it.
'98 LXi - Later Concorde gages (black w/ chrome rings)/'99 LX - LHS gages (white) - HIR bulbs