grill cleaning

I have used a pressure washer on a grill grate before.  It worked great.  If you don't have one handy, take the grill-grate to a car wash and use the hand sprayer on it.   

Then - as you suggested - a good seasoning is always a good idea.

You can try PBW (Powdered Brewery Wash) or OxyClean on the grates or other components that you can remove and fit in a tub. I use PBW to soak my smoker racks and such and they come out sparkling clean. (I am a homebrewer, so I have it on hand, but it is easy to buy online or at a local homebrew supply shop.)

From the manufacturer of PBW:

"Both are oxygenated Alkali cleaners. PBW, carrying numerous US Patents, set the stage by being a breakthrough product harnessing Oxygen as a solvent without being corrosive. Many other products now mimic that capacity but PBW was initially DESIGNED for a major U.S. brewery and goes much farther than just being an Oxygenated alkali.

In short, as PBW was built for the brewer, it has a package of chelators and surfactants chosen for that role. Chelation addresses mineral soiling and surfactants (detergents) also help the solution break down various soils. Products like the one mentioned and many others either have NO chelation or a very generic one not built for brewery chemistry, resulting in limited cleaning, especially over time. Yes, this can make PBW a tad more pricey, or does it? The recommended dilution for the home brewer is 2 oz per 5 gallons; spending about $1.75 to clean my gear with the finest alkali wash around seems reasonable to me (AND its biodegradable and yes, safe on aluminum and plastics as well as SS)."

Edited to add: comments about using this on grates and other things that you can remove and soak...

I cleaned up a couple grills a few months ago. One hadn't been used in a couple years and left out in the elements. The wife and I scraped the gunk out of the chamber walls w metal scrapper then I took a couple heavy duty wire brush for grills and brushed it a few hours. Sprayed it all down w some water on the grill and sides walls before hard scrubbing to limit the dust down and to get big stuff loose. Might wear a dr mask of rust is bad enough and have to lean inside to clean.
Got all the gunk off and majority of rust and scrubbed it down with paper towels soakeed w cooking oil to get the rest of the surface rust off. Got a big hickory fire going and get it super hot. I burned above 500 for a few hrs. Then i repeated it one more time the next week to get what I missed. Maybe overkill but it was pretty nasty. And it was cleaner then ever.
The cooker I cleaned is big enough to lay down inside so I went thru two brushes a roll of paper towels and a jug of vegetable oil. But worth the $10 and it was a free workout. Ha.
If I were to do it all over again I would burn it hot before I got to work scrapping and brushing stuff off. But I had lots of standing water in the cooker and wanted to get started.
Hope my experience somehow helps.