From your link, I was able to find a Russian site with diagrams for the IP which lists the rack damper bolt p/n A0029978545 SEAL RING

I was only able to find that seal ring on ebay so far. https://www.ebay.com/itm/Mercedes-300CD-300D-300SD-300TD-Fuel-Injection-Pump-Adjustment-Bolt-Seal-Genuine/352092278506?epid=1233829650&hash=item51fa55ceea:g:R~AAAOSwTM5Ys~Qe

drum roll ........... prices range from $29 to $45 for 1 o-ring

Are you kidding? Is there an alternate p/n that's cheaper?

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked