I've never done well with the stop leak, either. I wouldn't depend on it for a diesel system. Depending on skillset, time, and need, repairing yourself may be the way to go. I learned how to replace a radiator on my Buick because I had to. Once you become acquainted (Watch as many videos and read as many forum threads as you can find), it's not too bad- just a giant step-by-step.
Best of luck!
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