I'm too in the school of doing reasonable preventative maintenance on my schedule, and most important, location:)!
I'd go ahead and replace the battery. If it's an 8D, I was given a tip to look at CAT 8D batteries, as it had the highest CCA of any 8D that I could find. It's also Maintenance Free. Not the least expensive option, but I figured we'd get 8-10 years out of it, so that little bit of extra for cost upfront, gets spread over several years.
Been in for about 18 months now, and I've never noted any cell outgassing, which I like.
Good luck on your choice,
Smitty