posted by Miyoki instead of Kimura-san for the past activities on 24th April.

The gasket surface of the removed IFI flange was visually inspected. Based on the visual inspection results, the following three points are estimated to have caused this flange to leak.
1. scratches on the gasket surface of the flat flange with copper flange (thin vertical scratches can be observed when shining a light on it) One location
2. Scratches on the metal gasket surface (thin vertical scratches can be observed when illuminated by light) One scratch
Possibly traces of 1.
Uneven traces on the gasket seal surface If the gasket is tightened properly, the trace will be a circle of uniform width. Since the traces on the actual product are narrow and wide, there is a high possibility that the initial tightening of the claw clamps was not uniform.

Here are the countermeasures.
Since the instructions call for the flat flange with copper flange to be returned to the original mirror plate instead of using the copper flange, repair of the scratches on the flat flange gasket surface will not be performed. Instead, a visual inspection of the original mirror plate gasket surface is performed before installation. In addition, the gasket will be changed from a metal gasket to an elastomer gasket.