I finally took the lens out and take it apart yesterday. It had oily aperture blades and was stuck open for many years. It took me almost 2 days to get it done. Everything seems to work now. The only thing I am not too happy about is that the glass now is not as spotless as used to be. There is no way I could keep dusts from getting there. Before I started I could shine a flash light into the glass and there was no dust inside. Now I can see some. I will have to live with it now.