as it's an '05 you've gotten more life (in yrs) out of your clutch slave cylinder than a lot of Inmates have.
Oberon makes the best slave cylinder for the LC8 engine. Superior seal (not an o-ring or stack of o-rings) and the bleed valve is built into the banjo bolt so it always catches & holds the air bubble for easy bleeding
I use 10w fork oil, CJRacer likes Mobil 1 syntho ATF.
DON'T go back to the mineral oil...
I'd order a clutch master cylinder rebuild kit 50302032000 & do it all at the same time- the mineral oil tends to pick up & hold the aluminium alloy debris and the seal lips get worn. Just flush your line & wash out your master cylinder reservoir to get rid of all the nasty junk. You'll have better feel as well once you're done.
Also, when you replace the clutch slave, pack grease around the back of it inside the black plastic spacer; this will stop water/chain lube/dirt from getting in there and causing this problem in the future
As for the master cover, it is better to get a Phillips bit that will fit your screw well; then put it in an adaptor & use a ratchet/breaker bar to twist on the screw. Using an impact works but can also damage/break the master cylinder/mount. New screws with a touch of moly grease to stop them getting stuck again. Don't overtighten! I also loosen/retighten the screws on all master cylinder covers from time to time to keep them free
950 Adv 'S'
'87 KLR650 - +170K miles
"looks like you've had a lot of fun on that bike..."