Bulova 1971 Oceanographer

My first repair project, has had a hard life.  Purchased with no strap and looks like someone had tried to pry the onepiece case open, crystal cracked and water damage.
Removed the crystal expecting to be compeltely rusted out only to be amazed by the 11BLCD.  Planning to service and get back to running condition, lightly polish case while leaving the dial as is.  Balance moves freely but is very sluggish.   Inside case printed 2891 and stamped W GERMANY.  Thought this was an Oceanographer "F" untill I found the ref image from Andersok on another post, now unsure if "F" or "S"