I don't use the guide tubes any more, I'm pretty sure they were just mildly snug. I found it a lot easier to hang the spools of filament from a rod above the printer. It makes changing the filaments a lot easier as I don't have to get behind the printer to do so.
Yep, the spring holds the filament tight against the drive gear and pushing on the lever gives you room to insert or pull out the filament.