This thing has been growing slowly over the past year or so as I've put off the paint job and bodywork. It's definitely malignant and I'm worried about the Mound's health now. I've heard this is a common spot. Are there any support groups out there for the Mound?

Right on.

 

where it's at!

 

Ive never seen anything like that before...Not there anyway...

~T.J.

 

That's a bit weird. Normally rust is first coming through at places that have water/moisture traps. Like under the rearseats, or storage bins. Or for the hatch: in the raingutter (or whatever you call it) especially if the drainholes are not clean. The pic you posted, shows rust on a spot that, as far as I can judge, is not an moisturetrap, and is normally not prone to rotting like this. I've seen some bad RX7's by now (rainy climate overhere) but this spot is not common. Or at least not before the wheelarches are gone, fenders fall off, hood breaks when you open it, eh well, you get my point.
Still, pretty unpleasant for you...

 

That's more prone to happen along the hatch itself, just under the weather stripping.
Get that ground out and sanded to bare metal quick and at least primered, coz it's looking like that spot will have a hole soon and get worse from there.

 

Brown, it's more common than you think. 3 of my 4 1st gens have cancer in the same spot. Look at the underside of that area and Ill bet youll find the whole area has at least surface rust, specially on the spot welds. Get to work on the mound and save her b4 it's terminal!

 

Don't have it on mine, but I've seen that before.

 

Mine wasn't that far down, but I had to replace a good chunk of the rear hatch area because it was rotting thru and fallingout in chunks.

peace

 

I've got some rust there only because the morons who had the car before me took the spoiler off and then didn't patch the holes that were left behind...-_-

 

MINE HAS A HOLE IN THERE!!!

exactly the same...get it fixed ASAP I'm getting mine painted next year

 

that's got a hole already... I can pretty much guarantee it with my body working experience (a lot).

Jeff

 

yeap it's even got puss coming out of it.. yuck!