Cleaning seal residue from viewfinder

A recently acquired camera has what appears to be the residue from the mirror damping cushion on the viewfinder. The viewfinder is not removeable but I can reach with a cotton swap.

What's the best chemical to use? I typically use 91% iso alcohol for the residue when replacing seals but not sure how that will affect the plastic viewfinder.

I also plan to clean the mirror. Again, iso alcohol with a light touch.

Thanks.

The alcohol should be fine.

You will make it worse whatever you use. The underside of the screen is usually a very fine fresnel lens and the muck will just get spread into the grooves so you'll end up with visible rings in the viewfinder.

On the mirror, if there is no sticky deposits then spectacle cleaner (the non-alcohol type) is best but the alcohol should do no harm.