Yes, you can feel the looseness in the valve guides when you replace the valve stem seals. I used compressed air to hold the valves closed and also had each piston at TDC so the valves could not fall into the cylinder. After I took off the valve spring and seal, I turned off the air pressure and wiggled the valve stem to check the valve guide wear. It is kind of a judgement call whether the movement warrants valve guide replacement. I could feel a small amount in each valve guide and figured it was okay. I thought of using a thin wire, like a guitar string, to gauge the clearance but was afraid of scratching the valve stem or guide.
Replacing the valve stem seals is not a difficult job on the M103 engine. I replaced my valve seals with the expectation of doing a complete valve job in a year or two. My car has about 130,000 miles and still has the original head gasket and valve guides.