Waist level viewfinder cleaning advice

[Gott23]

So, I've just received my Pentacon Six (what a beast!) and an Exakta RTL 1000 (it's diminutive cousin) in the post; both with waist-level viewfinders.

Now the Six is pretty clear for its age but the Exakta's is quite dusty/dirty, despite the rest of the camera being rather mint.

So just to ask, what's the best way of cleaning these things?

Any advice appreciated.

Cheers.

[spleenone]

Hi there,
Any photos of that condition? You mean that glass inside waist lvl finder? Ground glass?