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reetings,

The 1998 CL500 is equipped with the M119 engine. Experienced a pronounced tapping or ticking noise originating from the driver's side valve cover region. Uncertain if the source of the noise is the plastic oiler tubes responsible for supplying oil to the camshafts.
The noise diminishes after a prolonged run, but if the engine is left running without any activity for around 5 to 10 minutes, a loud ticking sound reemerges.

The oil level is satisfactory.

Is it inadvisable to use an engine flush, such as Forte, before an oil change because of the car's age? Considering the possibility that it may be a congested hydraulic lifter.

Alternatively, you may choose for a fresh oil change and filter, using a totally synthetic 229.3 MB specification.

Thank you.

The oil tubes are very likely to be the cause.

What is your location?

Indeed, I am optimistic that the worst possible outcome is the one we are attempting to avoid. I am now located in Oxford.

If the tapping sound were caused by the cam oilers, wouldn't it be consistently audible? ... after an extended period of running, the sound ceases, only to reappear after a brief period of idling.

Using 1/2 quart of Automatic Transmission Fluid (ATF) is a milder method for cleansing the engine.

Occasionally, under certain conditions such as higher RPM or extended operation, a little amount of oil may flow into the tappet via the tube. However, the majority of the oil will simply flow out from the exposed end of the tube.

Removing the cam covers to inspect the tubes may be done in around 30 minutes. Upon inspection, it is immediately apparent if the tubes are damaged.

While I wouldn't consider myself a specialist, I can confidently state that plastic oiler tubes are a more prevalent problem compared to the probability of a tappet malfunction.

That is a logical approach. I will first attempt a treatment/flush and do a fresh oil change. If the issue persists, I will proceed with the next appropriate step.

I will return with the result.

May I inquire about the mileage accumulated since the last oil change?

There have been around 300-400 occurrences since last August.

I fail to get the rationale of changing the oil once again. I am certain that the issue is related to the tubes.