I had a similar issue, I ended up getting the lens back together, it took maybe 12 hours! Yep, every night for a few hours for maybe a week I would sit down study the mechanics of it and managed to get it completely apart and cleaned all the elements. Getting it fully apart is no easy task and I can't remember anymore how I did it. Repair is going to be expensive but you must get this lens back to life! It is the fastest MF lens ever made! You could always send it back to Mamiya or KEH for a clean/fix, for a few $ hundred....

Below was my drama re this lens, I eventually got her back into production (with the aperture working too) and have been thrilled since. There is some GREAT advice below....I wish you the best as this is a lens to get back into the field, the N is the best one too...
http://www.apug.org/forums/forum51/9...-1-9-lens.html