The driver side cover can be repaired with enough determination & patience.
I was in the same boat about a year ago (not quite as bad as your rusty cover pic, but leaky enough above #6 cylinder to burn a plug wire).
Here's a picture of my solution: cutting off the old flange, using it as a template for a new flange made out of 3/16" stainless flat stock.
It was my first stainless welding job that wasn't exhaust pipe. The whole project took about a week of nights, at least 20+ hours. It failed multiple leak tests until I got everything stitched sufficiently, with plenty of burn-throughs. I'm glad I sandblasted thoroughly, which revealed pinholes below the PCV port that also leaked.
Even with short stitch welds, the whole thing warped horribly and shrunk across the short side. I over came that with a couple hours back and forth to a 50ton press to spread the long sides back into spec. Then another few hours with a hammer, a vice, and finished with a flat file for a uniform sealing surface.
Quite a challenging project, but 11 months and 5,000 miles later, I'm happy with the result. Leak free and still looking good.
If I were to do it all over again, I would still have cut off the old rusty flange, but I would have made the new one out of 1/8" mild steel. Grind off the upturned outside edge, then find someone with a bandsaw to cut it off as straight and flush as possible. Use the old flange as a template on a single sheet of steel for the outside edge, then the valve cover shell as a template for the inside edge to be welded. Carefully cut out the new flange with cutoff wheels and/or jig saw, but leave a couple webs across the middle for stability until all welded up. Tape the PVC port, and fill with water to check for leaks. Finish weld, leak test, repeat. Check for flatness with a good straight edge, table saw platen, or surface plate. Cut out the webs, then drill the mounting bolt holes. Surface prep, prime, & paint.