Remember the current needs to flow in both directions and it is possible for one side to be blown and the other side still be fine.
Here the reading is .968 and well within range. You are allowed roughly a 10% variance from one side to the other so .968 and .973 are well within that spec at a 0.5% variance.
Despite being a relic, this isolator is still operable. If however you have an old isolator like this, and you keep your boat at a marina, I would strongly advise upgrading it to newer ABYC compliant unit. The other alternative is to regularly test your GI to ensure its operation.
My personal preference for GI's are the DEI isolators. I feel they are the most robustly built GI's on the market and you don't pay any more for them than you would another "fail safe" brand.. Again DEI has had ZERO GI failures that were not failed "safe" and this includes lighting strikes...