Hi Bruce:
Most of the end grain sealers,even if they do not stain the material, will cause holdout of any further surface treatment you might use. Neatly applied all do a good job. I assume this is green timber and perhaps a water based poly would work for you. I have been using whatever the final timber finish will be be for sealing mortises and end grain. I know others that use the latex based end sealer popular with log builders that can be stained later. Wax performs the best if you can be careful.
I'll ask around, but try the www.