Derailleur play between cage and knuckle I have a Shimano 2300 rear mech that's done about 10,000m over ~7 years. Lately I've had trouble getting clean shifting and find myself constantly twiddling barrel adjusters... I'm certain the cable tension is good and (by my eye) the mech hanger is straight, but there's a certain amount of play between the cage and the body:



Will this affect the shifting much and, if so, is it repairable, or time to get a new mech?

EDIT
Closer shot of the hanger, which does look like it has a slight bend in it, now that I can zoom in this close without my long-sightedness furring things over somewhat.
How worn are the cassette and chains? How old is the shifter cable. 

In my experience the order of things that cause shifting issues are chain wear, cassette wear, cables first. In my mind these are all considered consumables and replaced regularly. Derailleur hanger, especially if unknown history, is a likely suspect 

Last is derailleur itself.  At 10000km on a Claris it past its 'economic life', so I would not be worried about replacing it.  The play in the video is a bit more than I would like, but I hesitate to say it is definitely the cause of your shifting issues.