The mower is old (YT12/16D) Series 4 Tractor with a 41" double blade deck. The deck has 4 pulleys. One of those pulleys is attached to an Idler Arm and the Idler Arm has a Idler Arm Spring which attaches to the underside of the Arm and the other end attaches to a bolt thru the deck. My problem is that this spring keeps breaking at the deck bolt. Usually breaks 2-3 times a year. I have replaced the two pulleys on that side of the deck and replaced the idler arm assembly. I have greased the heck out of all of these parts. This last time I replaced the spring I realized that the nuts that hold the spring on were not correct and bought the correct ones with the spring. Put everything back together and mowed my 1ac. yard 1 time and the spring broke again.While this mower is old the motor is strong (Briggs and Stratton)and the mower deck and body are in very good shape other than this problem. I am about on my last straw and could use some help before bringing out the shotgun.