O-ring on the crown
Can you change the o-ring on the digital crown? Mine came out.
The link above is to the iFixit teardown of the Series 2. In order to get to the digital crown, you would have to completely replicate the teardown (see Step 16).
Then, you would have to figure out a way to remove the digital crown
replace the gasket, and then put it all back together again. This would not be a trivial repair, and would require all new adhesive gaskets as pointed out by @danj above. Additionally, the waterproofing aspect of any new digital crown gasket would be dubious. Might be okay in the rain, but I wouldn't take it into a pool.
I cannot find a link to a replacement gasket. So you can either find a parts-only Series 2 and use its gasket, or you can try to find a gasket that fits to provide some protection. Here is a link to standard watch gaskets: https://www.esslinger.com/watch-gaskets/