Your point is well taken. I don't know what a 2504D looks like or what kind of pump it has, but the guy seemed like he knew what he was doing (he may have the equipment you mention) so I told him where to get it. I used to have pumps professionally done (and still do) as you say, but I was driven to open my first Stanadyne in the 80's due to a group of P.I.A. rebuilders in N.E. Ohio. When the I.H. 6.9L came out, they were good runners. The injector pumps were terrible. They were so bad and were replaced so often that the price got down as low as $242. New. From International. Well, that party ended after a while and pretty soon the only good deal you could get was from a rebuilder, and by that time the price for a rebuild was back up around $500. The thing that ticked me off was, now they won't even take the top cover off for less than $500. You know, it was all or nothing, claiming the fuel would contaminate their test stand (whatever), the unit had to be completely broken down and inspected. The trouble I was having with this particular pump was that it wouldn't shut off. They began yapping about excessive clearance in the metering valve, having to replace the hydraulic head... that's when I left. I went home, took the top off, didn't find anything wrong, put the top back on, it was cured. Just some little quirk in that linkage, about once a year when it wouldn't shut off, you take the top off and jiggle the linkage, and it was fine. Another time, had another 6.9L pump built,(different truck) this time shopping for warranty instead of price. I was promised a year. Drive the truck for an hour, shut it off and it wouldn't start again until it was stone cold. Rebuilder said the gear train was worn out (at 33,000?) and to advance the timing "a little bit". At the end of 5 days (one month before the warranty was up) it wouldn't start at all, hot or cold. Took the top off the pump and found a broken solder joint on the ESO coil. Called rebuilder, said he would only warranty the pump if I took it off and brought it to him. So you see, there's 2 pumps I had to fix myself because fuel shops tried to B.S. me. As for major repairs, a Roosa/Stanadyne can be done at home in many cases. For one thing, when a new hydraulic head is ordered, it comes in a plastic cup, properly adjusted. Any adjustments that must be disturbed during disassembly, I make little gauge blocks for, so I can put it back together as it was. Will my pumps pass California emissions? Probably not. Was I lucky? Probably so. If it has plenty of power, doesn't smoke white at idle, or smoke black at high idle, I got what I wanted.