Pretty sure you just need to buy a new seatbelt, not just a release button. And it won’t necessarily be a Winnebago part. Winnebago doesn’t make seatbelts they just buy them from some 3rd party.
Here’s one… but NOTE I don’t know if this one is the correct one for your 30-yr old motorhome or not. You’ll need to search.
You could stop by any nearby junk yard that has RVs in their lot and maybe find one for a few bucks. Captain's chair seat belt assemblies with the clip in belt with a push to release red button are in millions of RVs. Salvage yards would have them too but expensive.
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'02 Winnebago Journey DL, DSDP, 36' of fun.
Just look up the Chasis and you should be able to order a seat.belt receiver
It's probably a Chevy P30 workhorse Chasis. Check with an auto parts store, junk yard or o use WWW.ROCKAUTO.COM., Partsgeek.com?
Any other auto parts aite.