Temps ain't bad fer the ambient temp in the UK when you posted - My DCE's idling at about the same.

Have you knocked a heatsink whilst cleaning it? Northbridge is a prime cause of high mobo temps if the thermal paste has hardened & been disturbed.

Also - Just taking the panels off is more likely to make things worse. Think about it: Whatever fan(s) you have are now trying to move a whole roomful of air instead of a caseful! You've removed any flow there was & the air is just hot & stagnant.

If your PSU's at the top rear of your case & draws air in - Put an exhaust fan at the front bottom of your case to create a flow through the case. If yer PSU is at the top rear & blows air out - Put a fan at the front bottom of your case to draw air in.........

Depends on your case & component layout as to yer best solution, but ffs put yer side panels back on!

Buy it a 99, it'll be fine lol.