I've done a bit of searching through old threads but didn't come up with much. Guess the D4E isn't exactly in the classic realm. 

That said, I have a lead on a D4E SA 29X. I've always had a hankering for a nice ag crawler, but such items aren't common in this area. What are the common issues to watch out for with these? I did read some reference to oil migration in the transmission, but no particular details. The machine in question has about 4500 hours on it. Being as they're like hen's teeth in this area I'm 99% sure that the crawler was used on a potato farm. 

Also, are there any online wear charts for undercarriage? I hesitate to ask about value as there are so many variables.

Thoughts and information are greatly appreciated!

Welcome! A fellow member which calls himself D4e, has owned MANY of them and I consider him the expert on the D4E's. That is how I purchased mine. 29X00827.
I do not know much about them; BPetty on this BB used to have one, but had issues with the final drives overheating.
Mine I believe is a 1977 model equipped with 6 roller frame and wide pads; and VHP. I use it for disking here and playing with scrapers.
Please tell us about the one you may purchase and some pictures if you have any to share. JM

As I mentioned initially I'm almost 100% certain this one has spent it's life on a potato farm. I've seen in the field a few times over the years.

Best I can tell it's just the standard 96hp, not the 140hp turbo type. Looks to have three hydraulic remotes. No pto or 3 point.

The only price reference I can find us a couple the Zimmerman has listed. Both of those are 140hp, and one has a brand new undercarriage. I'd venture a new uc alone is close to $10k these days.

I've been in touch with the seller and plan to check it out next week.  
 

I have had up
to 8 D4E SAs at one time 25 probabley over the years . This one looks non turboed . it has the good trans group 3 V 3121 . The only common problem over the years i have had is transferring oil from the steering clutches to the final
drives . I have always had a thing for D4 E SAs . pm
if we can talk on the phone . I have a running list of 29x and 70 i keep adding to

I readily admit my ignorance when it comes to Caterpillar engines. The tractor in question is naturally aspirated, which to my understanding puts it around 75hp. Is the 95hp configuration simply achievable by swapping the exhaust manifold, adding the turbo and adjusting the pump? Or is it more complicated?

You would need to check parts books for comparable engine parts like pistons, bearings and for sure the turbo version would require oil cooling jets for the pistons.

I met the owner after work today to take a look at the D4. Overall it seems like an unabused example. Sealed Cat tracks, certainly some wear, but without dimensions and a track gauge it would be tough to speculate exactly.

Started right up and seem to run fine. It was probably comical to watch me drive it as I'm used to a power shift John Deere. Only stalled the Cat once 😬.

The first iffy thing I noticed is that you have to kinda grind it into gear. Acts like the clutch drags a touch, or if there's a transmission brake it isn't engaging effectively. The other major hiccup I noticed is that the steering brakes are much more effective turning left as compared to the right. There again, could be a minor adjustment issue. Tach is inoperative. Presume the cab AC would need work.

As I'd surmised, it spent the last few decades pulling a potato planter. They quit the potato business a few years ago, so no need for the crawler.

Right now the price versus everything else isn't favorable to me buying it. I need to get some answers to the nagging questions at hand.

From what I can see the undercarrige looks good. Plenty of track adjustment left, bottom roller flanges a long way from pin bosses. It will have an oil main clutch which are known to drag when cold, even with a good brake. Those items you are concerned about are minor although steering brake wear could turn into a job if it's not just adjustment. Your not going to find a perfect 42 year old tractor.

Very true about any used piece of machinery, adjustments and repairs are bound to be needed. I suppose on the wear issue it being naturally aspirated is a bonus, were it a fire breathing VHP that spent it's life doing heavy tillage then there would be a lot more concern about wear. Pulling a four row potato planter for ~150 hours a year isn't nearly as worrisome.

I suppose at this point there are a couple other hesitations. First being that there's not a particular reason that I need the crawler other than a lifelong attraction to crawlers. An IH 706 would be cheaper, have similar horsepower, capable of road travel, have 3pt and pto. The second is price. Realistically I could get a D5B SA for a third less money, but there is the not so cheap issue of shipping.

Lots of things to consider...