They usually get grooved pretty well which in most peoples opinion does not affect the chain tension much or more importantly do they have the risk of self-destructing like the upper rails. I did the lowers on my 420 at 125K because I ended up pulling the engine to reseal the heads.

It is quite a bit of extra work to change them, I wouldn't worry about it too much.

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Chas

Had a 380SL, 450SL, 380SEL, 420SEL, 500SEL

Got a Euro 500SEC right now.