Bidders routinely request an oil-filler-cap 'dance' video as a compression check, but knowledgeable commenters (citing mechanic Pierre Hedary) argue it is unreliable, is only valid with the heavy original metal cap, and that turbo crankcase vacuum can skew it. The recurring counsel is that only a proper compression test reveals engine health.
The blow-by 'cap dance' test is discredited
Mercedes-Benz W123 · buying