What's a Combat Mechanic? That's bullshit. Don't get into bullshit. Whatever you do in any branch of the service will be deserving of respect. We'll know if you are full of shit, so don't be. I don't associate with many vets because I never knew while I was in that there were so many special forces people. I never even heard of special forces while I was in, and now everyone was in special forces or was a sniper. My dad is a Vietnam vet and served as the VA administrator for his county and accessed the records of everyone who came in to his office. That didn't stop them from trying to bullshit him. Through 5 wars, there were no supply guys or Motor T guys--just 8 million Scout Snipers and Special Forces.
I was in the Marine Corps from 1986 to 1996. I was a field artilleryman. We had M101A1 105mm and M198 155mm howitzers. We moved them with M813 and M923 trucks. We were airlifted by CH46s with the 105s and CH53Es with the M198s. We had Motor T guys that drove our ammo trucks and did the maintenance on our vehicles. Cannoneers drove the gun trucks, which I did, but when the shit broke, Motor T guys fixed it or replaced it.
There are tons of specialized jobs in the Marines. Not that many people are in combat arms jobs. From an artilley viewpoint, we took our gear to different units that calibrated tools, repaired our optics, assembled our ammunition, painted our vehicles when we went from green areas to desert areas, refueled our vehicles, built our boxes for shipping our gear, repaired and set up our radios, providied our weather reports for daily firing data, guided us through combat zones as traffic cops, provided us security during moves through hostile areas and even infantry, who are no special forces, hitched a ride with us at times and gave us the addition confidence and security of having another 150 rifles pointing outboard as we traversed risky areas.
Don't worry about boot camp and such. You ever watch What About Bob? Baby steps. There ain't nothing complicated. It all comes at you in bite-sized chunks.
Special Forces? Combat mechanics? Combat Supply Specialist? Combat Dental Assistant? Christ...dude, I hope you get to be full of shit. Anyone can be a marine. It's more about committing yourself than it is about being a difficult thing to accomplish. Even when what you are doing is obviously stupid, you just do it and don't think about it. You will make it through. Let things come as they will and deal with them when they arrive--Baby Steps. Don't worry about it. Don't be a bullshitter when it's behind you.
I don't know much about Motor T, but every unit has vehicles and a Motor T section. All of the vehicles are diesel powered, so just like your local dealership, you won't do any of the work on the important components. You will pull off the assemblies and send them in for repair. That doesn't mean you don't have to know how to troubleshoot--you do. It's not like a vehicle has 10 parts and you just take off the bad one and swap on a good one. Shit breaks in all sorts of unusual ways and you are going to do more repair in the field with whatever you have on hand than you will swapping parts.
If you end up there. Who knows. You can sign up for decorating birthday cakes for the Marine Corps Ball and end up in graves registration stacking bodies. It's a box of chocolates.