valve sticking in the guide is the usual.
especially as you say you HAVE replaced the valves. Not all valve stems are the same thickness and can vary by a few thou - which is enough to make one stick.
You should IMO be able to spin the valve freely up and down its shaft, it should also be able to seat fully and come out fully with no binding. I do this and ensure the components are dry!
Look for abrasion in the guide, and the valve stem. Also make sure there is no fouling of burnt oil in the guide.
If the valve stem proves to be straight by rolling it along a sheet of glass, buy an adjustable reamer and slowly and carefully ream the guide. clean fully with soapy water and a small bottle type brush to make sure there is no traces of loose bronze/iron from the guide.