Leather does not stain itself, it must have been done by something else. If you have a soft absorbent leather (one that absorbs moisture readily) then anything that has stained will be in the leather ans you cannot clean it out. You can only clean of...
No it did not come with a diesel engine, but it did have fine Corinthian Leather!!!
Yes you can, but you may need some modifications. We ran a National Park Service diesel powered boat on 100% bio diesel a few years back. We had problems with the fuel hoses getting soft and sticky, but had no problems with the engine running. Howeve...