My 91 had started making a roaring noise in 1st,2nd and 5th gear,so I took it to a transmission shop to get it checked. I was told the tranny was in VERY BAD shape ,and that they wouldn't rebuild a manual trans older than 10 years. Five transmission shops refused to rebuild it. At the time I worked at a national auto parts store,so I looked up a rebuilt one. Price was $2400 , BUT, supplier did not have one in stock. In fact,I tried every place that was suggested to me in the U.S. and got the same answer. Nobody had one,and I had just about given up. About 9 months later I rode with a friend to a repair shop that specialized in foreign autos that just happened to be about 5 miles from my house. I had totally forgotten about this place because its kinda way off the beaten track. I saw a wrecked Pathfinder in the salvage yard and casually mentioned to the shop owner the trouble I was having finding a 5 speed manual for a 4x4. He stopped what he was doing,walked over to a corner and looked at several transmissions sitting there and says," YUP! I thought I still had this one! Its yours for $400,and I'll install it for $550 more." Just got it back from him a few weeks ago and she runs perfectly now.
So , for me , the hardest thing to find was a 5 speed manual for a 4x4.
By the way,this guy has several Pathfinders and D21 pickups of various year model on his yard and said he has access to several more that a friend has so if you are having trouble finding something,hit me up and I can check with him. I've already purchased several other items from him and am going to get several others in the near future.