The OM-1, 2 and 2SP are built at least as well as the 3 and 4. It's the double-digit OMs such as the OM-10 and OM-40 which are the consumer-grade bodies. That said my OM-2SP is the only one which ever gave me any trouble, the ISO dial is intermittent.

Switching to "B" does not disconnect the batteries - I've tested that on an OM-4 and OM-2SP, the current draw on "B" is the same as other speeds. I have an early OM-4 and don't find the battery consumption a problem. It's a small price to pay for having the camera instantly ready to take a shot at any time without having to bother about switching it on.