What did you do to your Fiesta ST today ?

[WolfDampf]

I think hitting the washer with a hammer would defeat the purpose of a washer designed to deform to fit the surfaces of the parts being joined. Instead you'd have a washer conformed to the hammer.

That's my thoughts too, never heard of hammering it

 

[Stubborn Approach]

The banjo is installed with a new washer. You tighten the banjo until the washer feels crushed & wont turn anymore. Tap the banjo head with a hammer & the banjo will tighten a little more, creating a solid seal.