I ended up taking the lens to a local camera store and the gentleman there was more than helpful. The lens was taken apart quite easily, The ring with the Pentax 50mm marking was loose and it came out without trouble. The three screws came off next and the front element was off. the marks were not on the front element but between the next group of glass. That needed some effort to twist off but once off the three pieces of glass were easy to remove. A wipe with a new microfiber cloth cleaned whatever the brown marks were. The guy also used a little bit of some mild soap to clean it and the rest of the glasses were cleaned by simply blowing on to it. Eventually the all the pieces looked clean though after assembling we noticed a slight smudge on inside (only visible in bright light). Anyway that was left to me as a take home task ...
The lens looks clean and I think I am keeping it..
Here are some pictures taken in sunlight after cleaning..
Thanks for all your help and suggestions.