KEH usually specifies any shutter problems in the item description, so you have the option of returning or exchanging it. Most of their Contax bodies in inventory now seem to have some type of problem. Contax repair techs seem to be scarcer than those for Leica, so that may be one reason why there are so many bodies in need of repair.
I purchased a IIa from KEH earlier this year and it has functioned perfectly, so I suspect it has been serviced recently. It's extremely clean inside and out.
You can also try exercising the shutter a bit to see if the speeds even out, but the camera probably needs to be serviced as other problems may start cropping up.
They are very nice cameras to shoot with and the postwar Zeiss lenses are great.