crush washer questions

[blackestate]

Can you reuse crush washers? If so how do you tell when they are bad?
I have a leak on the fuel filter at a crush washer.
And I think that my trans leak is from the crush washer, not the dipstick tube. How do I clean up the crush washer area that looks like it has stuff imbeded in it?

I am new to the whole crush washer thing.

thanks