RawPwr (thrash?) - that seems to be a UIBI - they use "S" to control the relay (switching).
Besides, if yours has worked fine for 8+ years, how can it be wrong?
If I am right, then the Cole-Hersee S-type isolate is equivalent to a relay - eg, gnd - #85; S/alt = #86; batt1 & bat2 = #30 & #87.
bratnetwork seems to have a "smart" version which is voltage sensing. They are fine until they have problems. They also cost more than the UIBI, but are the only common commercial option for stator etc systems.
The cost for ~200A-400A capacity should not exceed $20-$25 for the isolator itself.
(Smart isolators are usually more expensive with inferior performance depending on user desires and application.)