Brake cleaner works well but it tends to evaporate fast. If you're not quick at spraying it on and working the action to aid it in flushing out the goop it may not work that well. Especially in hotter conditions where it evaporates all that much faster.
That's where I like a "slower drying" solvent. Or my favourite cheap and easy general purpose gun cleaning mix, Ed's Red. The recipe is an easy Google or Bing or whatever away.
The trick with this is to soak down the cylinder with it and then spin the cylinder and repeatedly work the ejector. Continue dipping the cylinder and crane into a dish of the Ed's mix or some other solvent and working the cylinder by spinning it and working the ejector repeatedly until it has a chance to work out all the gunk. If it's really bad it may take a few times. So be patient and keep repeating this dip and work until it frees up. Then repeat it a few more times just for good measure. Then tip it up and allow all the goop inside to drain out.
No solvent is good for our skin or internal organs. Especially if we'll just about be bathing our hands in it. Wear nitrile gloves when doing anything like this and your body will thank you later in life.