Original 5D sensor repair question

In 2008 I bought a 5D, it was my first high end camera, and shortly after I botched a DIY sensor cleaning. There is a smudge on the sensor that will not go away even after two professional cleanings at my local camera shop. Not an issue with shallow depth of field, but for studio work above f/8 it's a real annoyance. I am thinking I will need to send it into Canon for a sensor replacement. Or there might be a protective element in front of the actual sensor that can be replaced instead, not sure.

Anyway, does anyone have a similar experience and can give me an idea what to expect cost wise? Part of me is thinking to just get a new 5D Mark2 and give the mark one to my kids as is