First of all, thanks for all your help. You people are amazing.
I was finally able to remove the old switch. I had purchased a 1 1/16 deep socket and a crows foot wrench, both of which were not useful. There just was not enough room between the exhaust manifold and the starter.
I then purchased a 1-1/16-Inch Extra Thin Wall Wheel Protector Impact Socket
https://www.amazon.com/dp/B006L23AQ2 that almost worked.
On my next visit I came prepared with tools to completely remove the heat exchanged, but I tried loosening the nuts first. I was then able to get the socket partially on and after a few taps with a hammer I had enough grip to turn it with a breaker bar and I was able to remove the switch!
I had already purchased a replacement switch, but it also needed a 1 1/16 socket. I went to a couple of marine shops and everything they had also used a 1 1/16 socket. I went to an autoparts store and a very helpful woman let me look at a few switches. I ended up selecting a MasterPro 2-8000 switch as it only used a 7/8 inch socket.
Since it's used for Honda and Nissan, I assume it's the proper thread.
The only other difference was that the MasterPro used a bullet connector. It was easy to install using the 7/8 socket and the alarm sounded properly when I turn the key. Once the engine started, the light and alarm when out.

I took the old switch home and put a ohm meter on it and sure enough it was always open. I had tested the first switch I bought by blowing compressed air into switch to confirm it would open under pressure.
I tried it with the old switch and of course it never closed, but a considerable amount of oil came out, so I'm hoping the switch was the primary source of my oil leak.
I have no idea what pressure is required to open this switch, but when I shut the engine down, the alarm goes off instantly, so it seems sensitive enough. Either way, it's better than a disconnected switch. All told, I spent about $50 on various tools and $10 each for the two switches.
Here a look a the defective switch. Does anyone know if this is the standard switch for the M35? I suspect it's not.
Thanks again for all the help!