I like the 15 and 30 KW's. They are a good, dependable gen set. The white engine is a workhorse. I worked this gen set a long time, and found the engine to simply great. Problems like your fuel in the oil, are very rare. About the only complaint I had was some of the white engines had been "rebuilt" so often, without the crank being replaced, that on some engines, you needed to put smaller front and rear main seals into them. If you replace the seals and the new, standard seals start to seep/leak, that what needs to be done. The engines were being reworked in Utah, and CECOM got the boys there back on line. That's a long time ago. So probably no problem now.
On the electric side, once again, good and dependable. What I would do, if I were to want to have one for my house back up, would be to procure some of the electric boxes, the SP relay box, the A5 card and so on to keep on a shelf for a rainy day. The nice thing about it is that the 15&30 kW use the same parts, mostly, so there is a greater parts pool to dip from. I like the 004 and 005 simply for the fact that that it's way simpler then the new mep-804 or 805.
The short answer to your question is yes I would use a 004, and no, I don't think parts are a problem, if you got smart an found some spares. Most electrical problems on this set are DC, and mostly in the SP relay box.
That's a really great synopsis, and very helpful Sir. We ended up picking up both of those MEP004's. I was able to get one to fire almost immediately on ether for a few seconds (after adding new oil). The other one seemed to turnover very slow, and wouldn't pop at all. The battery cables were completely missing, guess somebody didn't want anyone to even try and start it? I was also curious if you knew why every 004 that doesn't run (whether private sale or on govplanet) seems to be missing the ip and or fuel strainers? Do they cannibalize them for use elsewhere? Have seen this over & over again......