Graham, do you have a photo of that washer?
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Graham, do you have a photo of that washer?
Attachment 25947Attachment 25948Attachment 25949Attachment 25950Attachment 25951 There is a small hole in the middle of lid & along with the washer that has a groove cut that allows air out. you can get a washer & use a hacksaw to cut a groove in it, regards Graham, New Zealand
Why the small hole? There's plenty of space in the lid clearance hole to relieve air pressure. I don't think I've ever seen sufficient fluid in mine to need a drain hole. I don't think it would help, but I guess it wouldn't hurt.
I made my cut washer out of stainless so I didn't have to break a plated surface.
Thought the small hole was factory.
Mine not only has the small hole, too, but there also is a plastic socket. That comes first, then the washer (grooves facing down towards the plastic socket), then the nut. Apparently avoids scratching the reservoir lid.
https://up.picr.de/43370674yx.jpg
Now this all makes sense. Thank you Graham and Konrad for posting the pictures.