Hmmm. I haven't seen that cap before.
Typically, the older ones are black but have P/N 996.106.447.00 stamped in them.
The newer ones are p/n 996.106.447.01 (or .02 and are usually blue).
What does the underside of your cap look like? Here's a shot showing the two OEM caps. Original on left, revised on right which creates a better seal.
No crust around the bleeder valve?
If no, good sign it's most likely the cap.
Start w/a new cap and possible a pressure test.