keyproblem

My 2003 CLK has had a intermittent problem with the key not turning on, 4 times in the last 5 years. Each time after inserting the key a number of time it would turn. Then no problem for maybe a year or so. Thursday last week key would not turn and had to be towed to MB dealer. They indicated the EIS needed to be replaced. Today when I went to get the car they tell me the steering wheel lock will not work. Symptoms are the same as last week. Key inserted, you hear clicking sound in steering wheel but key will not turn. I had both keyes and neither one works. Is there a why to test the EIS switch or are they just replacing parts until they find the problem. They now say the part needs to come from Germany and I should get the car back the first week of December. Please help with ideas. Thanks