Depends on your definition. 'They' used to differentiate between 'navicular syndrome'(unexplained heel pain) and 'navicular disease'(with bony changes). These days however, I think it's a general thing in professional circles to refer to it all as 'navicular syndrome' but xrays are needed to see if/how much it's progressed to bony changes. You cannot tell from xrays, what damage there is, if it hasn't yet reached bone remodelling & calcification. Soft tissue damage, which if chronic, is what causes the 'bony changes' needs MRI or ultrasound to be seen.First off you need xrays. You cannot tell if its navicular without x rays.
For the seller to admit to 'slight navicular', I imagine the horse is indeed clinically lame, at least sporadically, and has been seen/diagnosed by the vet about it, be that with or without rads done.does that mean sometimes she is lame ? Id you have the money for special shoes and pads