The way I did it was take the hood off, very easy with a helper, it's not heavy.
Remove the window washer tube, remove 4 bolts, which you can match up by the paint where the bolts were removed.
Flip the hood upside down on a table with blankets or towels to protect the paint on the hood.
I tried the air tool 90 deg. 3m white brissel pad to remove what was left of the old hood pad, (that was not on there when I bought the car). That worked somewhat, but as this was my first try at this I would use a razor blade paint scraper first. Then use the white pad to scuff up and clean the underside of the hood lightly. (mine was not oily).
I used a shop vaccum to clean up as I was scraping.
After you get the old stuff scraped off, use a damp rag to clean up the left overs.
Fit the NEW hood pad to the hood (NO glue) mark the new pad lightly with a paint marker in 4 places, front, rear, left and right sides on the hood seams.
Take the pad off.
Put the pad somewhere safe to spray it, and upside down.
I used masking tape and paper to protect what I did not want sprayed with the glue on the underside of the hood.
I sprayed the 3M 08090 19 oz. as the instuctions suggested, up, down, sideways, took 1 can, plus about 4 oz. of the 2 nd. can to do both the hood and pad. Probably 1 can would have been enough.
Ok, the help left, I had to put the pad on myself, I went for it, not bad at all, just line up the marks, front, rear. if you do not press on the pad you can reposition it. Once your marks are lined up, front, rear, start pushing from front to rear, then one side at a time, center to outer edge. Your paint marks should line up on the sides also.

If I left anything out, or not right, please fill in for me.

Edit: Napa had the 3M 08090

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1985 300D California w/cat. (257,000 + Miles)
1980 300SD (208,000 + Miles)