Finish is corroding and damaged, I never used anything harsher than hoppes on the barrel which did not splash on the handguard and simple green wash with warm water for the rest of the upper and lower and I have been doing that for years now without any issue on my DD handguard, YHM upper, Spikes upper and lower, and my Colt lower.
Simple green is not good for aluminum, perhaps you’ve just gotten lucky on your other items. Use something else would be my recommendation, it doesn’t look like it’s developed a problem yet.
From Simple Green’s FAQ: “However, caution and common sense must be used: aluminum is a soft metal that easily corrodes with unprotected exposure to water. The aqueous-base and alkalinity of Simple Green All-Purpose Cleaner can accelerate the corrosion process. Therefore, contact times for unprotected or unpainted aluminum surfaces should be kept as brief as the job will allow - never for more than 10 minutes. Large cleaning jobs should be conducted in smaller-area stages to achieve lower contact time. Rinsing after cleaning should always be extremely thorough - paying special attention to flush out cracks and crevices to remove all Simple Green® product residues. Unfinished, uncoated or unpainted aluminum cleaned with Simple Green products should receive some sort of protectant after cleaning to prevent oxidation.”
Edited:
You may as well be swimming with your carbine in seawater.
Washing the upper and lower? 
What is it a vehicle? :sarcastic:
You always here that over cleaning does more damage… and I’m always like… HORSE SHIT… but then these kind of things pop up! :eek:
A simple rag should suffice for almost all of your exterior cleaning. Chalk it up to a lesson learned. At least you have a great rail and didn’t damage anything other than its purdy face.
Seriously you guys don’t thoroughly clean your upper and lower with warm water and a good degreaser like simple green? or dishwashing soap? I’m just OC about it I guess I do that to all my FA and for years have kept all my FA spick and span.
Reminds me of some Marines rifles I have seen downrange, I always wondered how they cleaned their guns to the point of removing the bluing etc.
…now I know.
I was at one of Paul Howe’s classes a few years ago and there was a Sgt. from the 10th Mountain Div. who stated that they sprayed everything down with Simple Green and then showered with them. I imagine the rifles were looking pretty rough at the end of the tour.
Bingo. Who cleans the OUTSIDE of their AR?
C4
Further perpetuation of the reputation that Marines can break anything. :blink:
Uh, nope.
I only periodically clean the BCG and bore, the rest may get an occasional wipe off with a paper towel.
I do run plenty of quality lube though.
Dont you get the outside soiled with sweat in your hands, grease or carbon buildup and some other elements that could do more harm then having it too clean as I do.
Uh, no, I don’t think I have ever “cleaned” the outside of an AR before. I might wipe it down every once in a while but that is it…
Probably a good idea to change your thread title from LT problem, to Simple Green problem.
They could fuck an anvil with a rubber mallet, as my uncle would say 
ML, as far as I can see no bare aluminum is exposed. Both LaRue rails I’ve seen have shown the same ‘film’ in the same areas. The mounting section and the QD sockets are epoxied in place; it may be possible squeeze-out forming the film you see. That or perhaps some form of protective coating to seal the anodizing. At any rate, see if you can gently scrape it away with your fingernail. The film on my rails was easily scraped away to leave a uniform black surface. Never been a concern since.
I would try to scrape it gently, but as the violent reaction to simple green here I am having second thoughts now maybe I was just lucky and my luck run out, I use simple green from my Ruger LCP to HK P90 and to my 3 M4 of different make and models and this is my first Larue as well on all that mix, I’ve had DD handguards, YHM upper colt, magpul lower and a spikes tactical upper and no damage with SG
I don’t think the simple green has caused a violent reaction…
I’m also wondering about cleaning the bbl under my larue rail. It a stainless noveske bbl. will the simple green and hot water harm my bbl?
Nope and doing so would get you a nomination to the OCD hall of fame.
No offense hoss… but lighten up on the cleaning the exterior of your weps.
This made me :sarcastic:
My Larue rail looks like that. No solvents on the outside of my rifle. Just normal wearing.