I have this older 300mm Symmar convertible which is my prime 8*10 lens. About 2 years ago after shooting misty snowscapes I saw internal haze inside both the front and the back elements. Since there was almost no contrast (the over cast sky and the snow functioned as a huge reflector) I could see no advert effects on the prints, but I did not like the haze. And AFAIk it had not been caused by the temperature differences or condensation

So 2 weeks later I opened both elements from the front and took the front groups out and very carefully cleaned the haze (it seemed almost oily sticky stuff) with 100% ethanol and finished with lens cleaning fluid. Let it dry thoroughly, removed as much dust as possible, and placed the groups back in. These groups seat on rings, and although a tight fit, came out en went in smooth. So I assumed that they were properly seated again. Images shot afterwards do seem to confirm proper sharpness (I only contact print my 8*10 negatives though).

Thus far the lens is still clear (I will check tonight again..;-)..)

Perhaps an option for ones older lenses were warranty in not there, and cleaning might be to costly,

best,

Cor