changeing element on Neff oven?

Hi I am attempting to change the Fan element on my Neff double oven. All the screws on the backplate were rusted in and I have had to drill them all out, now I can see that the element is held in by screws that are rusted as well, do I have to drill these screws out as well, as I will need some method of fixing the new element in place.

This is all caused because my oven has a self wash system which uses steam to clean inside oven and Neff have not used stainless screws
My top oven does not have steam clean and the screw heads are perfect. I have tried talking to Neff and have found them useless and uncaring.
any ideas?