why don't you check with David aka Fatigue at Personal Services Offered.
He can help clean the lens of fungus and hopefully can help you with the max aperture problem.
if u been using quite some time and its only happen lately.. its alway good to know what is the last event u did... but if u juz get it and its like this.. probably u can ask the person that gave u this... i am sure there is a veri good explaination for this... if u hv another lens or able to borrow one... u can try it on to see whether u will get the same results.. i dun think its the body still cos its unlikely the body has software bugs...