280 miles ? Looks like you're about 80K overdue for a chain to me. I drove my SD about 10K without checking and changed it when I found the instructions here.

It's not that big a deal. I like clamping the chain to the cam gear with vice grips which have rubber hoses slid over their tips.

I covered everything with rags and ground the master link off the old chain. I also crimped a new link to join the old and new chains then ground it off to install another new link to finish the assembly.

The worst part is finding a chain crimping tool to borrow.

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84 300SD
85 380SE
83 528e
95 318ic