The Pure Rock Slim is not a very bad cooler if you are not overclocking, and should be able to keep the temps within acceptable limits...
http://www.guru3d.com/articles_pages/be_quiet_pure_rock_slim_cpu_cooler_review,9.html
The fact that it is not doing so, might be because there are other factors playing in the mix. Your ambient might be higher than normal, or the thermal might be wearing out or the chip might be pushing harder than normal. I would start with reapplying fresh thermal paste and keeping the ambient cooler than it is currently. Also the air flow of the case needs to be checked with the fan alignments in proper order for intake and exhaust. The case doesnt look too bad, but I have never used it so, i would go by the user feedbacks which seems acceptable. If all else fails then a better cooler choice would be the Cryorig H7.