I used a plastic based truck bedliner product. Different products are avaliable at most auto paint stores. Very durable, chip/scratch resistant, not harmed by most solvents including brake fluid (tested real life bleeding my brakes).
The application involved stripping the old tar, de-greasing, priming. The product is shot using a low air pressure undercoating (Schutz). Three quarts covered the engine compartment and front trunk. Cost was about $100 for material and the schutz gun was $35. Hands down, for someone who works on an engine far better then any paint.
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