I'm getting ready to do HDs on a 10 year old C with 137k miles. The rears do sag about 1/2 inch. Would you suggest new springs? If so, all around?

If not, will spring pads suffice, or will they just cause the spring to compress more (which I would think is not the best idea)

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former: 83 300D, 97 C230, 93 400E

current: 08 C300 Luxury , 92 500SL