It may not be the same issue but my DM9 did exactly the same and I thought it was the LPR but in the end it was orings. I'm not an expert but I believe the LPR sends lower pressure air to move the bolt forwards and backwards and that air is vented on the forward stroke. If the orings don't seal the low pressure air trying to push the bolt back leaks around the seals causing a permanent leak similar to what your describing. Apologies if this isn't the same as your fault but only advice I can offer at the moment mate.
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