W123

While replacing my rear axle, I unbolted the shock from the top (per the instructions). Unfortunately, I just left the washer on there while I lowered the shock with a jack.
When I got the axle installed in the hub, and raised the shock back to its normal position, I heard a clunk and looked to realize that the large washer on top had fallen off. I have looked in there the best I could and can not seem to find it. I have a temporary solution on there currently which consists of two washers that are slightly smaller in diameter than the correct one. The substitute is only there so that the whole assembly doesn't fall down, and I would like to get a correct one on there as soon as possible. Preferably before I start driving it again. (it's parked right now while I fix a few major items)

my '82 300D stumbles when starting in hot or cold weather. i replaced the glow plugs and reamed the pre-chambers. they had minimal carbon build-up. i checked engine (1 degree stretch) and IP timing (24 degress BTDC) and they are both ok. compression is 24+ bar across all cylinders with 96k original miles on the clock. injector release pressure is low (1750 psi) and i plan to replace the nozzles and bump the pop pressures to 1950 psi. could the low pop pressures be the root cause for the stumble starts, or is there something else i need to check?