I've cleaned it up, including the PSU, i washed it in the shower so low pressure and just let the water run through it, and it got 90% of it which I'm satisfied with. It's now in the Oven at 200F for drying. The case I washed with a mix of Dawn Dishsoap and 99% isoprophyol which worked wonders to remove most of the tar staining on the case, its now not as obvious, but the only way I think to make it completly disappear to to get the original IBM paint to paint over it with
I felt safe washing it as the shop that had it, stated they have been tripping over it in their storage room, he said since about 2003/2004. So I think in all that time whatever the capictors once stored is long since discharged.