If it isn't using oil yet...what is the motivation for replacing the guide seals?
I am not sure if this quote is reasonable or not...I assume that the cylinder heads are being removed to do this. If so, in order to get to the guide seals, the valve springs and valves come off at that time...and the valve diameters and guide id's could be measured at that time. The valve faces could be checked as well, looking for wear, burned edges, etc. If the compression is ok, and it isn't using oil, why tear into it? If compression is ok, presumably the rings are in decent shape, the valves are sealing passably, and the guide seals are not leaking. Without dissasembly, if it makes normal power, compression ok, and minimal oil use.....this would fall into the if it ain't broke......category I would think.
Just an opinion. Good luck, dave