My bottom seat cushion has too much "sag" when I sit on it. I suspect broken springs. Is this a repair that can be done by a good tech or does the cost get prohibitive (i.e. should I just live with having to keep my seat bottom cushion inclined all the way "down" to keep the front in the right position?

Is this a good weekend project for a novice or are there special upholstering skills needed? In other words, I don't want to break (or tear) something that's just worn. Can individual springs in the seat cushions be replaced? All of my seats are like this to some degree. Thanks in advance,

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Robert W. Roe
1984 300SD 165,745 miles