You don't have a problem. Read the manual! You should never pull the trigger, it's not a Glock. Clear the weapon, lock the slide to the rear, lower the yellow sear deactivation lever, rotate the takedown lever, release the slide allowing it to move forward, and remove the slide from the frame. Just that simple. Will pulling the trigger release the slide, yes, but not by design. Reassemble in reverse order, install the slide, locking it to the rear, rotate the takedown lever to the up position, take a finger and push the sear deactivation lever to its upright position, or insert an empty magazine which will accomplish the same thing. Then there's the oil. Flooding the firearm with oil only creates a **** magnet. Every piece of dirt, dust, lint, or unspent powder will stick to it. It won't improve anything. Disassemble it properly, clean it properly, lube it properly, reassemble it properly, then go shoot it.

I've had at least 6 Shields in one configuration or another, and not one has required a trigger pull to remove the slide, and every one required you to "manually" lower the sear deactivation lever.

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SFC, US Army, Retired