f series oil seals

i have a s21esna and need to put in new oil seals. can i put them in when i put the two halfs of the power head together or do i need to put them in after i put the two halfs together. also the oil seals i bought are flat on one side and have grooves on the other. which side goes out?

When you put the case together use anaerobic sealer which can be bought in most auto parts stores. Now as far as the seals go always install the lip of the seal so the load or liquid goes against the lip of the seal. It really doesn't matter if you install the seals before or after you put the cases together. It just will be easier to install them when the case apart.