Sorry for the belated reply.
A friend bought a rather cheap Mongoose off eBay for her son's Birthday. He wants a project to do up, but is only eleven and I don't think he realised what's involved.
Upon seeing the BMX after it had been bought, I found the following problems.
1. The BB was loose.
2. The crank was at an odd angle
The BB and crank have been replaced from a donor bike
3. The headset had a bottom cup and bearings in the top of the steerer.
4. The lower bearing race was hanging out of the bottom cup.
5. The top of the steerer is threaded but doesn't have a nut.
A star nut and top cap have sorted the top of the stem/steerer.
6. There is a bolt missing out of the stem clamp (3 of 4 bolts present).
A bolt still has to be found (or 4, as the rest are rusty) for the stem.
7. The pedals are toast.
8. The 10mm rear axle is bent and we're missing 10mm x 25mm threaded bearing cup off one side.
A new axle should sorted by the LBS tomorrow, not sure about the bearing cup.
9. The lad wanted a gyro system for spinny things, but the bike obviously wasn't originally designed for this, can it be retro fitted?
As you can see, this is a project and a half for an average bike at best. I have no knowledge of BMX bikes and am flailing around a little in the dark, hence why I wanted to speak to somebody with more experience.