Great work, but it probably is time to change the sensor. As mentioned before, there are alternatives to the "overpriced" MB Bosch sensor. As indicated in other posts, the Ford Mustang 5.0 sensor is the identical 3 wire Bosch made sensor, you just have to do some wire surgery, which you appear to be quite capable of! I bought one of the the www.oxygensenors.com
kits since it was pretty much complete with shipping for the cost of rounding up the parts from the NAPA store. I'm waiting for a free weekend to get under the car to install.