If there are any old 671 engines that have the IP that is NOT lubricated by the engine oil you need to make sure that the IP oil sump is filled properly with oil (the old 220D and 240Ds I believe had them but I do not know if any 617s had that type of IP).

Most of the 617 Fuel Injection Pumps are designed without O-rings in the Delivery Valve area as the Crush Washers are in a different spot and do all of the sealing. If you did have O-rings to seal your Delivery Valve Holders it would be better not to change them until 1 of them starts leaking. The exception might be if you are going to use and alternative fuel and want to replace the O-rings with Viton ones.
The problem area on the IP is the Hand Primer that goes on the Fuel Supply Pump. The older ones with the hard plastic knob that you have to unscrew before you can pump tend to leak or allow air to be sucked in (fortunately easy and cheap to replace).
There have been a few members who have rebuilt their Fuel Supply Pumps but most see just to get a used one from the Junk Yard when they have a problem.

Since you have been a member for a long time you must have read some threads on timing chain stretch which also effects the IP timing as the IP is driven by the same chain. I think most cars including mine need the IP timing checked. Some day I will get around to checking it on my car.

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84 300D, 82 Volvo 244Gl Diesel