90 300TE, 4Matic light, steering angle sensor

[Barn]

90 300TE 4matic 159,000mi The 4matic light came on yesterday. It was reset by the shop the first week in Jan. They reported a steering angle sensor fault. After the light was reset it worked for about a month with great traction in the snow. I was told the steering angle sensor is no longer available for that car. Two items that may be important. Four new tires were installed yesterday, but I drove 30 miles after that before the light came on. I had collapsed the steering column all the way about five miles before the light came on. If this is related could it be a poor connection or a broken wire?

Will the light stay on even if the fault is intermittent?
Can I reset the light myself or do I need an MB specific scanner?
If so, what is the cost of a scanner and are there any aftermarket scanners?
Is the streering angle sensor hard to replace?
Should I bother trying to get one from a junkyard?
Any other sources for the sensor?

Thanks for the help. Barn