Salty
Thanks for the advice. The screws on my oven are also seized solid. I was planning to break them off and if necessary drill them out and replace the whole assembly; the assemblies under the hob, the burners and the screws. Do you see any problem with this approach apart from maybe costing more than a new oven. What kind did you end up buying?
The oven I bought was a Dometic Starlight with two hob burners, an oven and a grill. The addition of the grill within the overall height of the cooker meant that with the pan retainers, it protrudes two or three inches above the top of the worktop. Additionally and as mentioned in my previous reply, the cooker is slightly narrower than the old Techimpex cooker which meant making a timber frame to reduce the space across the top opening for the cooker and getting a stainless surround made up to fit the new opening. The extra work sounds more difficult than it was in practice, but having made the timber surround I was then able to hand that to the stainless fabrication shop so that they had a clear idea of the size of the opening for the stainless surround. The gimbal mountings for the stove were then added to the stainless surround, and I have used a long thin bolt to go through those mountings to ensure that the cooker cannot go "walkabout" in the event of a knock down.
I didn't think it worthwhile to try to sort out the broken off hob burner retaining screw, and so the old oven was removed and given to a friendly boatyard foreman who has a sideline in metal salvage.
I have a complete spare and virtually brand new Dometic Starlight gas cooker available for anyone prepared to have a go at sorting out a faulty thermocouple on the oven gas control. Make me a sensible offer and it's yours, with the proceeds going to the Lifeboat service in UK.