I have a Gundlach 8x10. Whether or not the one you're looking at is worth $400 depends on a number of factors. The gears for focus adjust can strip. The tracks the gears drive in can be broken. The focus and lock knobs can be impossibly stiff or completely missing. The front standard can be rickety or possibly cracked. The glue in the entire thing may be failing by now.
Mine was in many pieces when I got it. I think someone dropped it down a flight of stairs.
I fixed the bellows, which had 10000 pinholes at every fold, by painting them completely with rubberized sealant. Then I painted that with acrylic paint (because the sealant stayed sticky, even after two weeks). I haven't used it in the sun (I use it to take pictures of my kids) but I think it's light tight,
Mine came with a big lens in a No. 5 shutter. The shutter was also smashed apart. The lens was undamaged. I had to find some screws to use in it and had to get a spring from a (also smashed) Polaroid SX70. The shutter works perfectly. It's amazing how little there is in a Betax No. 5 shutter.