Disassembling Optima 535 Sensor's lens?

Got one for €5 but the lens is not clean and it needs good cleaning.

Any idea how to disassemble its lens? Seems all the elements are in front of shutter/aperture assembly.

* Film transport is not smooth compare to Silette LK sensor, my another camera.

Erik Fiss has a nice write about the Optima 535 http://www.erikfiss.com/foto/cams/optima/e.html and about how to get into http://www.erikfiss.com/foto/cams/_articles/optimadisassy.html

Its fairly easy but I miss the spring on reassembly which tensions the small ball bearing.

Lens was not affected by fungus instead I presume the coating was damaged on the front surface on the lens. Or it was etched by the previous infection of fungus.

Complete disassembly was infact simple too. Found the spring which was holding the ballbearing and put them back.

Everything is good now expect the surface of the lens.

Any idea what defect is that?