I'm looking to do my first fluid change on my "new" '52 R25/2. The owner's manual says to use engine oil. I called Vech and ordered fluids (before I had the manual in hand) and they sent me GL4 80w90 gear oil. I understand the GL4 part...bronze parts, etc. But should I be using engine oil instead? I have no clue if the seals have been changed to accomodate the gear oil. I'm at least 4th owner, and probably 5-6th owner. The bike was in police service through the late '50s and '60s but I have no idea what maintenance or changes were made.