The camshaft is hollow and carries oil pressure. When the plug comes loose the valve train doesn't get enough oil at the rear of the head and you get a clattering. If it were mine I'd probably clean everything real good and press it back in with some red loctite. I think there is an updated part from M/B but I don't recall any specifics. If you're willing to pull the camshaft out there's lots of creative ways to repair it.

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90 300TE 4-M
Turbo 103, T3/T04E 50 trim
T04B cover .60 AR
Stage 3 turbine .63 AR
A2W I/C, 40 LB/HR
MS2E, 60-2 Direct Coil Control
3" Exh, AEM W/B O2
Underdrive Alt. and P/S Pulleys,
Vented Rear Discs, .034 Booster.
3.07 diffs 1st Gear Start

90 300CE 104.980
Milled & ported head, 10.3:1 compression
197° intake cam w/20° advancer
Tuned CIS ECU
4° ignition advance
PCS TCM2000, built 722.6
600W networked suction fan
Sportline sway bars
V8 rear subframe, Quaife ATB 3.06 diff