I'd put money on it just needing a good clean out in the flush side. One of our old vans with an electric flush would get bunged up with black bits if the fluid wasn't mixed properly.
We buy loads at work from RS tool-wise. Definitely not the cheapest for but us when suppliers have to be on the system and we get a little discount its usually easier.
Another point for tools etc is pop into your local agricultural engineers or dealers. Friend works for the local New Holland Dealership and they stock loads of good stuff, same for another couple of hire places.