Bosch HBN 642 -- single oven cycles and doesn't get...

I own a 7-8 year-old Bosch wall mounted single oven, HBN 642 A UC.

Problem 1: in bake convection and regular bake mode, oven would operate fine when used for shorter periods -- up to, say, 40 minutes. When operating for longer (say, 45+ minutes), the unit would stop heating and would not heat up again until completely cooled down. (I.e., the "heat" light would go out, convection fan would stop, no heat to elements, and unit would cool down, regardless of position of control or temp. switch.)

I attempted to troubleshoot by carefully removing and disassembling the "thermometer" and cleaning the contacts. Re-assembled and re-installed.

Problem 2: Now the unit only heats up to, say, 325, then cycles -- heat on, heat off -- every 5-7 seconds when the unit reaches 325. (Yeah, I probably made the situation worse.) Problem exists in both regular and convection mode, except the convection fan cycles as well in convection mode.

Would you recommend a new thermometer? New high temp. sensor? If a new thermometer is needed, do they simply install without any adjustment to the part?

Thanks in advance for your kind assistance.