I just replaced the brakes all around on my 85 300td (rotors, pads, master cylinder, hoses). I also replaced the two front calipers because one of the pistons was stuck. All of the calipers are fixed with no place to lubricate (don't think I would try). Maybe on a floating caliper one could lubricate the top slide and the lower bolt, but not the piston. My opinion is that you spend the money on the brakes and tires, your life depends on them.

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Paul

1991 300TE (280,000)
1985 300TD (432,000 miles - retired)
1976 300D (225,000 - retired)
1975 300D (165,000 - retired)