He's right. The actual wood isn't much thicker than a piece of paper. It is covered by a thin layer of clear plastic. Over time, this plastic fogs up and develops cracks. Two possible choices.
1. Replace the trim panel (expensive)
2. Remove the trim panel and wet sand with 600 to 1000 grit wet/dry silicon carbide paper. When all the cracks have been smoothed out and everything is dry, spray with 4 or 5 coats of satin sheen polyurethane. Not factory, but generally looks a lot better that before. Final product is a function of how much care and work you put into the rehab of the panel..

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Jeff L
1987 300e
1989 300e
1987 BMW 325