How do you remove dirt & oil from polished exterior

[Eagle & Bear]

We decided to drive to Alaska this year. The trip took us through the Yukon and on some dirt roads while it was raining. The AS was covered in a thick coat of mud. When we got to Tok, AK we used a car wash to spray off the mud from our TV and AS.

The heavier layer of mud washed off the TV and AS but there was a residual of what I presume to be oil and very fine particles of sand. I would like to clean off the aluminum but so far the oil & sand have resisted high pressure water, soap, WD40 and a full strength TPA substitute.

Anyone have a similar experience and know how to clean this stuff off without damaging the polished aluminum surface?

Thanks,