It was common for the disks on the front of old beetle solex carbs to pop out if timed incorrectly/too lean and the carb backfired. They were only peened in place with 3x punch marks.
Common fix is a 5p chemical metaled and again peened in.
that sounds good to me ,
years ago (back in the 1960's) my dads lorry shot a core plug out the engine block due to frost.
He got an old penny and bent it a bit, shoved it in the hole in the block then tapped it with a hammer, it stayed in there for
about 3 years and never leaked. might of been longer but he sold the lorry then, and told the bloke about the old penny.
ive seen lots of carbs and engine blocks where money has been used to fill in welch plug holes and core plug holes, probably cheaper too ha ha .
What's the exact diameter? I have a handful of Lithuanian "pennies" which are thin aluminium from a trip last summer kicking about. Handling aluminium coins feels so wierd, they are just too light. They got the euro over the new year so not even legal tender anymore!