One thing that works great for me is Easy-Off Oven Cleaner. I spray some into the cover and use a plumbers brush and cover the area's. I let it sit for 1 to 2 hours and wipe area with a damp paper towel or rag. If it is really built up several applications may be necessary. Then sometimes I will use the wire wheel on the grinder and shine everything up. The oven cleaner is in the $3.00 range and does a great job!

Bob