The eBay BEAR (bulk edit and replace) tool is pretty simplistic, can't do RegEx search/replace, has trouble with HTML tag sets sometimes, and has a 1000 character limit. Your problem script section above is 2½ times that limit.
396 listings should be under any "number of listings that can be bulk edited at once" limit that may remain in the various versions of the BEAR tool scattered around eBay.
You should be able to replace that mess with the BEAR tool if it is consistent (exact same format and content in a group of listings), but you would probably have to do it in multiple passes because of the char limit.
Because of the problem it has with broken tag sets you don't want to do it from top to bottom but instead inside out. In other words, remove an approx 995 char complete inner block of it first, then another approx 995 char layer, then the remaining outside <script> .... </script> that should only contain approx 600 chars.
In the case above, it looks like an approx 1300 byte block of the same script is there twice. So that narrows it down (if they are identical to getting that 1300 byte block broken into 2 passes under 1000 chars each. (if the two script instances are identical, each pass will remove both copies at once)
Might want to try a BEAR search and replace where you make a pass and replace the approx 600-700 byte section starting with
function() and ending with var runid = null;
with nothing, then a second pass on whats left, replacing
<script> and ending with </script>
with nothing.
Assuming the content of the script in the listings is consistent, that should get rid any number of copies of the script in them.
If that fails, shipscript has some wisdom and external tools:
https://community.ebay.com/t5/Tools-Apps/Bulk-Editing-Description-Problem/td-p/28072112
https://community.ebay.com/t5/Tools-Apps/anybody-else-struggle-with-the-eBay-bulk-edit-tool/td-p/275...
