I have the chance to buy a 10 to 15 year old Swarovski spotting scope. (Habicht AT80) (20-60 Eyepiece) Maybe slightly older? Buying it from an elderly lady who says she hasn't used it in 10 years. She was kind enough to let me take it home and try it out for a few days. The problem is when you look through the scope the image is a yellowish tinge. The outside lens surfaces look generally clean so I'm wondering if this is worth buying at all?