This Vehicle Needs Real Fuel!

I just got a brand new, fancy car! The problem is that it keeps telling me it needs REAL FUEL to function! I took a look inside the tank between both of the "Real Fuel Drums" and both of the "Gas-to-Battery Rechargers" and I'm having difficulty figuring out exactly what else I need in order to get my fancy new car going! What am I missing? Is there some other kind of fuel that would get me to work today?

Hint 1

There are two Real Fuel Drums (RFD) and Gas-to-Battery Chargers (GBR), each are opposite of the other of the tank.

Hint 2

The tank is pretty small and can only hold 9L.

It's been an hour, so here's...

Hint 3

The RFDs were on the up and down sides of my tank, and the GBRs were on the left and right sides.

Hint 4

When I filled my tank with Real Fuel earlier, it seemed like a little spilled out the sides. Oh no! I hope I didn't ruin my drums or rechargers :(

• Hi Mathgeek, and welcome to PSE! Since we have people from all around the globe, we usually add hints only after a full day; that way everyone gets to have a go on equal terms. Cheers, and Happy Puzzling!
– Bass
Commented Mar 9, 2020 at 18:05
• Next time I'll wait before putting any clues in :) Will do! Commented Mar 9, 2020 at 18:44

Hints 1 and 3 tell us to

put the letters RFD above and below the tank, and the letters GBR to the left and right of it.

Your fuel tank therefore looks like this:

We know from Hint 2 that the tank only holds 9L, and indeed, the grid only holds nine letters.

So how do we fill the tank with "Real Fuel"?

By literally inserting the letters of "REAL FUEL" into the grid, like so:
And the extra "U" in the middle is the final, missing fuel that your vehicle needs: uranium.

Plaintext version of the solved grid:

/RFD\
GULAG
BLURB
REFER
\RFD/

• >What am I missing? Is there some other kind of fuel that would get me to work today? Commented Mar 9, 2020 at 18:36
• And Clue 4 indicated rot13(gur jbeqf fcvyyrq bhg bire gur fvqrf) Commented Mar 9, 2020 at 18:38
• @Mathgeek Are you just looking for "uranium"?
– Deusovi
Commented Mar 9, 2020 at 19:05
• That is all that I'm looking for. Commented Mar 9, 2020 at 19:06
• You know, I was thinking that when I wondered what the extra "U" meant, and then I talked myself out of it. Whoops! Thanks for pointing me back in the right direction. Commented Mar 9, 2020 at 19:10