Rear lens of Olympus 100-400: How to clean?

Peter Heckert2 wrote:

The rear lens of the Olympus 100-400 is really deep inside and the opening is very tight.

What is the recommended way to clean this, if ever required?
Is there a recommended way or are there special tools for this?

It is even difficult to inspect.

I get a craft paintbrush wooden handle (for safety) and turn it around and wrap a microfibre cloth 2 layers thick around the wooden end and then insert and clean. Either with or without a drop of ROR or Eclipse cleaning fluid on the cloth. Recently I discovered Zeiss Pre Moistened Lens Cleaning Cloths... not to be confused with the Zeiss individual lens/ spectacle cleaning cloths found in supermarkets and chemists. The afore mentioned, as pictured below, can also be wrapped around the wooden handle as they are quite large. They clean superbly and almost always without any residue or streaking which then needs buffing with a microfibre.

In over 60 years at this nonsense, I have never-ever, ever found the need to go anywhere near a rear element of any lens I've owned, and that must run into hundreds.

The front element might get a puff, but very, very rarely.

Dave in Wales wrote:

In over 60 years at this nonsense, I have never-ever, ever found the need to go anywhere near a rear element of any lens I've owned, and that must run into hundreds.

The front element might get a puff, but very, very rarely.

The OP did say "if required", and I agree, that well recessed rear elements usually go years before cleaning is required. A friend of mine bought a well used but optically good Canon EF 400mm f5.6. She felt her pictures were a bit "hazy". I threw the protective filter in the bin... it was covered in fine scratches from poor cleaning. The rear element, really deep down inside, looked like a frosted light bulb it was so dusty... hardly any of which blew off with a blower. Wet cleaning was needed and the overall optics came up 9.7/ 10 and her pictures looked good after that.