My thoughts are the lack of use caused the pump to go. Some times life gets in the way of riding. I would bite the bullet and put a new one in and do the job myself or with some help from a mechanically inclined friend.
I have found I had fewer problems with my high mileage ST. I used to put 17-20K miles a year on my ST without problems. My High mileage ST (over 200K miles) had very few problems. Original alternator (40 amper), water pump, carbs never off, 5-6 year battery life and yes the original belt. Other than typical wear items (head lights, tires, oil, brake pads), I replaced a couple clutch master cylinder kits, wheel bearings, and rear shock. I also did the red wire by pass.
I have found I had fewer problems with my high mileage ST. I used to put 17-20K miles a year on my ST without problems. My High mileage ST (over 200K miles) had very few problems. Original alternator (40 amper), water pump, carbs never off, 5-6 year battery life and yes the original belt. Other than typical wear items (head lights, tires, oil, brake pads), I replaced a couple clutch master cylinder kits, wheel bearings, and rear shock. I also did the red wire by pass.