Here are parts
Replacement parts for KEBS207SSS04 models | AppliancePartsPros.com

Could not find info on the SS04 so the above and following data sheet is for a SS00.

Here is the data sheet
http://www.servicematters.com/d...0Sheet%20-%208303952.pdf

Are both oven temps low?
Well it does look like your temperature recalibration worked in a way now the convection temp is too high. This tells you that the unit was properly calibrated to start with. Also your temperature sensor is OK.

Does the unit come off of preheat and indicate that it is ready?
If this problem is only in one oven, it could be the bake element is shot.
Although I could not confirm that during bake the unit switches between bake and broil elements,many units do this so the temperatures in the oven are even. The data sheet does show that it uses both elements during preheat.
Use different settings to check that all the elements will come on especially the bake.

I did notice that the unit is less than a year old. I would not do too much messing with it as that may void your warranty. Might be best to get it repaired under warranty.

Note it could be the control board is toast which definitely would be a warranty repair.

If you do get it repaired under warranty be sure to keep all documentation as to what was replaced etc., just in case the problem re-occurs in another 3 months and at some point you have to fight with the manufacturer/dealer to have warranty extended or the entire unit replaced.

The tech's service manager is trying to convince him (and me) that there is nothing wrong.

If you could answer this question it would really help. Should a setpoint of 350 degrees hold the oven temp at 350 in either regular of convection bake?

How are you measuring the oven actual temperature?
Ovens display or a separate oven thermometer?

If you are getting it from the oven's display then I would say you still have a problem. The unit should bring the temperature to whatever oven temperature you entered and then it should cycle the elements to hold that temperature.
Besides you said it worked OK for the first 3 months.

Not sure how to explain this but hopefully the following will make sense.
The oven offset is just to vary the actual in oven temperature.
It does not change how the oven sensor and the electronics control the unit.
The sensor is just a type of resistor that changes it's resistance with temperature.
The sensor is 1350 ohms at 300 degrees and 1550 ohms at 350 degrees.

You set your oven to 350 degrees but actual internal temperature measured with a separate thermometer in the oven is 300 degrees.
Your oven is running too cold so you do a temperature offset/calibration.
Basically you are telling the unit that 1550 is 300 degrees (not 350) so it will continue to heat.