The front group comprises of 2 elements which are sealed together and the infestation is on the inside. I can't figure out a way to clean the inner surface. Has anyone had any success with it?
A simple lens consisting of one glass element can be used for pictorial photography. However, all lenses suffer degradation due to focus defects called aberrations. Lens makers have struggled with camera design since the beginning. They are unable to eliminate aberrations; however clever designs make them all but disappear. Since there are seven major types of aberrations, it takes a multi-element to mitigate.
A modern camera lens consists of positive (convex) and negative (concave) lenses sandwiched together. Some are made using hard dense glass; others are made using glass of lighter density. Some elements are air-spaced; some are cemented together. The cement must be transparent, non-yellowing, and it must have an appropriate index of refraction. For most of photo history, glue was made from the sap of the Canadian Balsa tree. Today’s lenses are cemented using an artificial resin. The older cement, being organic, acts as a culture medium that can support fungus and mildew. To overhaul infected cemented lenses, you will need to soak them in an appropriate solvent. After separation, you will need to re-cement using a glue with the correct index of refraction.
Such a task is daunting and likely unsuccessful unless the craftsman has an optical bench and special skills.