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spencerdd

I have an SPX-5 on a Catalina 34 sailboat. Other than an initial purchase warranty problem in 2013, it has worked well since 2014. However, this year, the boat falls off course very quickly... about 15 minutes under power on calm water and about 2 minutes if under sail or under any kind of cross wind. The pilot appears to be trying to correct course and the virtual rudder indicator gradually indicates more and more rudder being applied to correct the course but the wheel isn't turning. Eventually the virtual rudder indicator shows the helm hard over and doesn't try to correct course anymore at which time, the boat quickly falls 20 degrees and more off course triggering the "off course" alarm.
I have done the Sea Trial Calibration several times to try to correct the issue and also manually fiddled with some of the Dealer Cal parameters, especially Rudder Gain, Counter Rudder and Auto Trim with no improvement.
Compass position has not changed and the area is clear of interference.

I do not have a rudder reference transducer and have not had one since new. If this would correct the situation, I would gladly install one but why would performance change so dramatically over a year? Also, I note in paragraph 2.9 of the SPX-5 setup manual, it says the rudder reference transducer gives an accurate display of rudder position. I'm not concerned about the display of an accurate position but would hope the rudder reference transducer provides better feedback to the course computer to allow course to be maintained.

so...
1. would a rudder reference transducer solve this problem? If so, what caused the pilot to work well for 5 years.
2. software issue? If so, how can I correct this.
3. do I bite the bullet and get a new autopilot - maybe Evolution-100 (but why buy another Raymarine if my current one has failed after only 5 years?)

I appreciate your comments and assistance