On the old ZD series the major problem was the HST's failing, and mostly due to lack of maintenance and/or operation in really hot weather. I have heard of this issue but more commonly in the Southern states that see 100 degrees+ for months on end. But good news, I am told the ZD18's did not have many problems in that area, it was almost always the 21 or 25/28. And that problem has been FIXED with the ZD300 series and now the 1011's and ZD1211's which replaced the ZD300's.
The ZD18 was a good mower. Wish I had one.
