after 17 years of faithful service, I am embarking on a restoration project for my 1991 740 b230F sedan...

I have interior cloth seats which are now just showing some wear and tear. I noticed that I am getting a brown residue on the carpet, under the front seats. I am assuming that this is deteriorating seat cushion? Is this the warning sign that new seat cushions need to be replaced? The seats still feel fine, and I was hoping to get away with just some new seat covers.

The body really looks great - the only rust I have (a small amount) is on the top of the rear doors, along a felt seam. What causes this to rust? I thought I would dig out the rust and bondo repair (its a small area) and then even perhaps seal the area with a small amount of sealant (RTV?)

I would very much appreciate hearing any experiences and thoughts about the seat cushions/seat covers?/and upper rear door rust spots.

thanks!