I found my cheap oven very easy to take to bits to check stuff, etc. As it was very mechanical, it was easy to trace all the wires and work out what was doing what. In the end, I simply wired the SSR over the 2 terminals going into the rotary thermostat thingy, so to run it with the Pi, I leave the dial set to zero but turn on the main power and oven selector, or just use the temperature dial to run it in the old way.
Also, the main power knob is the mechanical timer knob - one hour max, so I just wind that up, then if something does go wrong, at least it will turn itself off after an hour.
For your oven - if it's a capiliary tube system, you might get away with bypassing the existing controller by simply buying a replacement tube +
the one on my Beko when I replaced it last year.
However, here's a suggestion - scrap the oven and replace it with a really
Then use the old one as a test-bed to play with, then retro fit the controller to the new oven (or swap them back) when you have Pi control :-)
Good luck!
Gordon