The '68 BBF Manual describes how to replace the top and window curtain, top only, and window curtain only. Also, there are somewhat fair plastic window cleaners out there to try before replacing the window. I gave away the bottle of the one I used and don't recall the name. Finally, I did multiple cleanings with spray degreaser and a hose plus a lot of putty knife and stiff brush cleaning on the underside of mine. With 175,000+ miles, oil and trans leaks, it was many fun hours.