The X300 is a significant upgrade from your LA110!Thanks for all the info. If the guy's yard is relatively flat, he's the original owner, and it hasnt been used to haul boulders, I'll feel comfortable pulling the trigger on it. My old 2007 LA110 also has the K46, has been abused over the years and just refuses to quit. My FIL uses it to haul stuff around his property and the transaxle never complains.
I say go for it if everything checks out. When you have time change the hydro fluid to 5w50 and you will be more than good. It requires removing the transaxle but its not terrible. I did my LT150 and it keeps going. I way over work that thing with a 15hp Kohler and it still keeps running. The X300 is a bigger better machine.