Oops. The red LED in the mantlet occupies the space for the gunner's telescope. All you need to do is push the LED out as it is normally a friction fit and the resulting hole is the correct size. The aperture on the other side of the mantlet that is missing on the HL Pershing is the port for the Browning .30 caliber coaxial MG. This port is smaller and should be around 3mm.

That's just my historically correct and anal answer.

Welcome to the forum and good luck with the HE Leopard!

-Harquebus