940 What's this bolt hole?

Heater pipe on my 93 940 sprung a leak so I had to pull the turbo and manifold. With all that out of the way, I noticed this empty bolt hole on the rear of the engine near the oil filter. Am i missing a block to transmission bolt, or something? Does a sensor bolt there on a different configuration?

You can see it here below that screw in coolant tube:

https://i.imgur.com/pGboCzK.jpg

We get this question 2-3 times a year. It is a left over from days gone by. Volvo used to put a pick up for a dealer service timing indicator in that hole. The magnets it sensed were still installed in the flex plates long after the sensor was eliminated.

Ah, very interesting. Thank you for the reply!