The early 149s of the 1950s have a long celluloid ink window, which takes on colour from the ink over the years. As long as it is a matter of deposits on the surface, patient soaking will help: fill the pen right up with clean water using the piston, leave it to stand, and change the water every few weeks. It is a business of months, but in many cases it brings a clearly visible improvement, and it calls for neither tools nor dismantling.
Where the ink has eaten into the celluloid, the damage is permanent. Windows in that state look evenly stained, often dark red; here even prolonged soaking achieves nothing, and the ink level stays unreadable. Harsh cleaners, solvents, alcohol and mechanical polishing are all strongly to be avoided, because celluloid reacts badly to them and can go dull, crazed or brittle. Anyone who does not feel confident about taking the pen apart should not attempt it: pens of this period are glued and press-fitted, and a broken barrel is far harder to replace than a cloudy window.