That brings back memories. Had a friend, a lifetime ago, who was a retired Marine. "Crazy Osteen" we called him.
To the point, WD-40 was the go to for his 700 BDL. No matter what we went through, he would shoot the entire weapon, optics and all, with WD-40 and set it in the closet. I followed his advice until I read an article, in Shooting Times I believe, stating that penetrating oils could work their way into optics causing damage. In the following ~32 years it has been Breakfree CLP for me. But everyone has their favorites. Got hard-sold into a tiny little bottle of some heavy duty gun oil for full auto and suppressed firearms, the last time I bought field pants. Asked for BF CLP and ended up with this product, which the salesman swore was a clean & protect all-in-one. Got it home, read the fine print and it is for lubrication only, no mention of cleaning. He was right about how little you need, a minuscule drop between the slide and barrel will lube everything barrel, slide, recoil spring, slide rail related. It lasts for... Well, on my EDC that one drop has never leeched off between range sessions. Also, the last few times I practiced at the range, I could not shoot hard enough or fast enough to cook it off. BF will cook off after a quick rapid-fire string.