Yup, I've had it happen on my 4200HST, twice it happened. It was an $8.00 seal that needed to be replaced on them. Labor of course was a little more expensive. I had mine fixed about a year ago, it is a very simple problem. My seal got a little dry, and also the dealer told me to always make sure you have the proper ballast on the back of your machine if you do plenty of loader work. I want to say it was about $65.00 to get it fixed. Not a big deal. If it is a very slow leak like mine was, you can still use your tractor, just got a few messy spots on the garage floor, so I had to lay down some cardboard til' I got it fixed. A little oil shows up a lot. Not the end of the world or nothing.
My advice: Get them both replaced at the same time, save on labor costs. It's not a whole lot of money.
