Oil or non-graphite type grease will work. Clean once or twice a year and lube. Some guys pack them some guys oil them and some guys just put some grease in them.
Most folks I know use grease in Ford or Tiger or Bulldog roller timers. Warning: Reproduction roller timers can be useless junk depending on who made them!!!! The best roller timers are old original ones made before WWII. Especially the original Ford ones.