Do not use grease on the D5 (as mentioned by Jetguy):

#1 the stock bushings are sintered brass on the slider blocks of the D5 series. They MUST be that because the outer rods both turn and slide.

#2 heavier machine oil is preferable to grease because grease plugs up the pores in the sintered bronze.

Sewing machine oil is probably the best thing in common use that would work. It is specifically formulated NOT to gum up like other oils and grease and become sticky over time. You apply some to a paper towel and rub down the rods. You do not need to go nuts and put too much oil on.

Further, periodically take a dry paper towel and wipe the rods to remove the black contaminated oil from the rods, then wipe with a fresh paper towel and oil.