Replacing the insert as Dan suggests is the least expensive way to go. Have you tried simply cleaning the insert with a product like CRC MAF Sensor Cleaner (AutoZone, NAPA, PepBoys, etc). It worked like a charm for me as the sensor wire was intact, just dirty. At $6/can, if your sensor wire is unbroken, you may want to try this first.

Bob

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Bob Jones
Bradenton, FL
'87 560SL-Sold
'99 SL500 For Now