Extract a mainly numeric string (ISSN number) from an arbitrary string

First post, really stumped here.

I want to extract the ISSN (publication serial number) from an arbitrary string.

The ISSN may exist in any of 4 formats:

12345678 - 8 consecutive numbers
1234-5678 - 8 numbers, middle dash i.e. between 4th & 5th digit
1234567X - 7 consecutive numbers, X suffix
1234-567X - 7 numbers, middle dash, X suffix

All other cases should be ignored.
For example:

1234567
123456789
123-45678
1234-56789
123456X7

My limited Excel skills would probably require a bunch of helper columns, so I'm looking for a cleaner approach, preferably with regular formulas.

If there's a big difference in complexity between a reliable method vs. something that usually works, I'd prefer collecting false positives vs. missing valid ISSNs.

Any comments appreciated.