The leather in my 450SEL is in fantastic shape, but the horsehair pad in the back seat bottom is heading south. What is involved in replacing the pad? How difficult is it to get the leather off and back on? I appreciate any and all advice on this subject.

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1978 450SEL (Pearl white, bamboo interior, 97k)
1959 Impala (2 dr. Hardtop, red, white int., 283 V8, 45k)
2003 Tiburon GT V6 (Ultra Sports Pkg. 3, red, blk int., 13k)