Curious about a small rubber cover on my engine block

I forgot to take pictures when I had my TMIC off, so I will do my best to explain it.

I was installing my AOS yesterday, and when inserting the "new" oil return to my crankcase breather, I bumped this rubber seal to the right of the breather (sort of directly behind the turbo inlet for TMIC, and behind and slightly to the left of the throttle body, located on the engine block). This knocked the seal off and a large gear was exposed.

The rubber cover is approx a 2" triangle shape, pushes in to seal.

I have never seen anything like this on cars I have worked on in the past. What is it? Are my assumptions correct that this hole is used for checking timing?

Thanks.
 
Probably a flywheel access cover

A goal is not always meant to be reached, it often serves simply as something to aim at. (Bruce Lee)
 
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