My eyes, my eyes! That's a very unpleasant image ...

Step 1: shop vac
Beyond that, I'd say get some products from POR15. Marine Clean, Metal Ready and then POR15 SILVER ... I ordered their "starter pack," but I would say you need more than that. As for welding/building up, I can't tell you a thing (I'll let the other guys help ya there), but whatever bare metal youre left with, clean with Marine Clean, prep with metal Ready and then paint over two or three layers of the silver POR15. I don't think you need to put a coat of primer or paint over top that, since the area isn't exposed to much sunlight, right?

__________________
1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)