Here is a link to the what I think is the best cleaning fluid for eyepieces and other lenses. I've been using this fluid for decades and have found it cleans lenses spotless without leaving residue. It's only ten bucks, but you'll have to pay shipping, A bottle will last a lifetime unless (1) you overuse it, or  (2) you're really young!

I'll always remember the instructions that came with my first Leica camera, "It's better to keep your lenses clean than to keep cleaning you lenses."

https://www.edmundoptics.com/f/edmund-lens-cleaner/11485/