Does anyone have any experience with or knowledge of anyone who has filed an Article 138 UCMJ?

The Senior Officer ,OIC or CO usually passes them on to the IG. That is when you find out there are two ( 2) types of IG. One working for the CO, and the other , outside the immediate chain of command, and that office can do some good. The "local" IG gets his or her OER written by the CO or OIC that IG works for. What do you think happens to "in house" IG investigations? They are reported back to the same chain of command you just filed your Art 138 with. You need to report Art 138 to the IG outside of the Command.

Which IG? The local command OF or the seperate Army wide IG? Go see a seasoned JAG officer first.

Yes, soldiers at the USDB, Ft Leavenworth, KS, while serving their prison sentences that had not yet been discharged, are still subject to the UCMJ. Some would use that article to harass the CO, of the DB and the CO of Ft. Leavenworth.
Fixed that by handing them their DD and BCD's and then marching them next door to the US Federal Penitentiary to serve the balance of their sentence.

Theres a form to request legal assistance from tds. Fill it out and go over what you have with the tds counsel. Let them advise you on the best course of action. Show them your evidence.

Ive invoked it. I won the battle and lost the war, but was comforted later finding out the SGM was a drunken wife beater and the CO covered it up. He was gone after a year and they pretty much left me alone after that. I can tell you I ended up with a relief for cause and an intimate knowledge of the appeals process. The command does not have to follow regulations in that aspect as the IG told me there is a specific redress for evals. You have no right to be counseled in a timely manner and if you piss off the CO you will have an inflammatory paper trail started against you. Know this: once you hit 17 years, you can come to work and put your feet on the desk just dont get insubordinate. You can't be kicked out of the Army for alleged incompetence.

If you are considering filing an article 138, you may certainly go speak over the subject with the TDS staff on the matter. You are entitled to assistance in filing one. You are allowed to also speak with the IG as others have recommended to at least get some point of view or advice on the matter. There's the issue of timeliness and giving your commander notice and opportunity to correct the action.

As a PV2 you should probably just keep your mouth shut and focus on maxing you PT and qualifying with your weapon.

Had an issue with a senior NCO once who was using his position and connections to ruin people. The IG heard me out, and once his name was brought up I was told that my complaints were on record and it wasn't the only complaint. The NCO was relieved by the end of the day and told to retire. Here is the deal, I am a chain of command guy, but when you can't use it and you know (beyond of shadow of doubt) that you have to "goods" on someone then go to the IG. It's your protection and they are experts.

actually did this,even though i proved my case,i was sent to the brig for 7 days,because a guy in my toolroom lost a flashlight for an hr,i was not,the supervisor,if you feel you must,hire a civilian or you ll get screwed

My old PLT SGT file one against the COG(commanding officer of garrison).
Nothing was seem up front in the public. But the COG Was denied his star that year for the blemish on his record. He address my PLT after a few month and apologized for the incident.
So there is hope if you have the right documenation.