I agree with Mark get it from a dealer, I purchased a Husqvarna RZ4623 in 2013 and as of yesterday I haven't had any problems with it, it now has 139 hours on it.
I would recommend a Husqvarna, to help we need to know how big your lawn is, I have about 1.5 acres I mow and the RZ4623 will do it in about 1 hour and 20 minutes, what I have is a residential with sealed drives which are Hydro gear EZT, they are used in a good bit of low end residential mowers, they are sealed but you can take them out and change fluid, I would buy another mower with EZT drives.
You can move up to low end commercial which will last longer but of coarse you will pay quite a bit more for it.
So how much is your budget ?