Have you removed all your cladding, There can be some big suprises.
I removed some of mine today.
The small piece behind the rear door On the front Rear quarter was difficult. I removed 6 today on 3 cars.
I found the top pulls straight out leaving the bottom in tact.
I pulled the top out slightly and sprayed 'simple green' to soften up the plastic.
I then use a hand held torch "plumbers" torch and applied heat briefly from a distance 2 times waiting in between.
One plastic piece about a quarter of a inch stays with the cladding, And the other plastic stays on the car.
Find the split between the two and use a large shank screw driver and pry straight apart, slowly.
This worked for me without any damage on the clips or cladding.
There are 4 , 1 in drains under the rocker cladding which most likely will require a wire brush and reprimer'ed.
A gallon of base coat or if you can get enamel is not expensive.

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1992 300d