Konica Minolta DiMAGE Scan Elite 5400 II Film Scanner

Have had this scanner for a couple of years now and was very happy with it.

Recently all my scans are dark by at least 1-2 stops and the colors aren't as accurate any more.

Could the CCD be going bad? Is there such a thing as a calibration slide that I can use to make global corrections? I've never been too good at color correction and having to correct every scan is a pain.

I only scan slides (Fuji Velvia).

Thanks