[JayJay]

I don't know about "aluminum-safe" or not, but I've found that there are two flavors of oven cleaner: old fashioned stuff (aka "extra strength" or "industrial") that is based upon lye (sodium hydroxide) and the newer "fumeless" or "fume free" that is based upon butoxyethanol compounds. I've tried both for grunge removal. The latter (fume free) doesn't work at all for me, and the former (lye based) works great. Scrape off as much grunge as you can, as ursus suggests, spray the stuff on, spray it again, then spray it again. Let it sit for a half hour or so, scrub with a wire brush until you get a nice disgusting brown foam, hose it off, and repeat if necessary. All the safety precautions apply.

I find I use a full large spray can or two for a short block. Best $10 spent.