why does my cooker burn baking on one side?

Model, Cannon Stratford. Approx 3yrs old. Burning baking on left side facing, especially cakes on 1hr bake. The gas engineer came & tested for various things, but could find no fault. Spoke to his manager, came back to check vent, again o.k. Said rubber around door could be replaced, this was done, & I was to contact on outcome. I have taken photo of cakes baked today, & when in town, will show photos to engineer.
When I baked cakes today I put brown wrapping paper, cut to size , to see if this would help. No it didn't!!
My scones, shortbread, in for 20/30mns, are not to bad, but I do turn around trays 10mns from end of cooking.
The last sponges I made,the dogs got them!!!!!!!!!!
They weren't light texture, crispy was no use.
So do you think you could give advice on what I could do, in light the of engineer has tried everything.
Otherwise I do like my cooker.

Margaret Duncan
October 2011