I have a 1946 Commonwealth Skyranger with steel wing struts. What is the best way to check the inside of them for corrosion? The outside of them have been stripped and look perfect. I have done a "TAP " test and the sound is constant. I have tilted them and do not hear anything rolling around. I have access at the base where the adjustment screws in and nothing falls out. I can use an automotive boroscope but it only goes in about 18". Any more ideas ? Thanks