I also have a Seymour Solar filter used on a C 90 and 90 mm F5.5 Refractor. bought from Rother Valley Optics , some fairly long time ago. The Instructions give advice on checking for Pin holes (Hold the filter with the inside towards you and outside towards a 60-100 watt soft white light bulb.two feet away from the bulb. Any pin holes can be blocked using a fine point felt marker , small drop of paint or typing correcting fluid. AS many as 20 touch ups per clear aperture inch can be made with no adverse effect on performance). Seymour’s then say that pin holes are rare in their quality products. Hope this helps
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Supporting amateur astronomers since 1890