Advice on Buying — JD 690-C or JD 690-D LC / Is the 690 D a Better Hoe ?

I looking at (2) different Excavators, a 690-D with about 9,XXX + hours; 690-C with 2,5XX hours. This 690 C has set for a long time because it was vandalized. Recently, all the glass was replaced, the exterior was re-painted due to spray canned graffiti. I'm a retired big truck/ equip. mechanic with some operating experience on -- CAT 312 C, and JD 320, CAT 977-H, CAT D6-N and other equip. . I've checked some of the spec's. out to compare the 690 C to the D model. The 690-C was the 1st year for Joy Sticks, see below: (690-C Spec's. ** @ 2500 PSI, pump flow @ 84 gal./ min., Swing Speed 7.8, RPM Travel Speed 1.8 MPH, Eng. 6-466T @ 134 HP (690-D Spec's. ** @ 4060 PSI, pump flow @ 50 gal./ min., Swing Speed 13 RPM Max Travel Speed 2.4 MPH, Eng. 6414T @ 132 HP http://washingtondc.craigslist.org/nva/hvo/4303730805.html ** I've Placed a Deposit (above) on this 690 C ** Price is $ 15,000.00 firm. I will have it looked at on Mon. or Tuesday. Known faults, gauges don't work, No info. on engine temp., oil pressure, etc.; other wise... the 690-C is reported to operate without problems. It has a 30" bucket on it an in good condition. ** I'm planning on loading up about -- 150 tandem truck loads of shale with the hoe I buy. I'm building a 2 mile road on the side of a mountain and need to supply fill shale for the mtn. road. Also, it's tough shale to dig, sparks (like concrete) come off the teeth when you dig it. ______________________________________________ End of 690 C Info. __________________________________________________ JD 690-D LC with Mech. Thumb. http://www.ebay.com/itm/161199850488?_trksid=p2055120.m1438.l2649&ssPageName=STRK:MEBIDX:IT The last owner, used the JD 690-D to clear his land, it was not serviced that much, he used it and dumped it. I provided a link for eBay and video is included. You will see that it (blue) smokes quite a bit. The seller told me that the engine is starving for fuel. Maybe fuel filters, or ?, hard to say. The blue smoke is rings and could be a pending overhaul job. The price is $ 11,500.00. The 690 D may be sold, but the deal may not go thru with the with the engine problem. ____________________________________________ End of 690 D Info. _____________________________________________________ My Question: I'm zeroing in on the (late 70's) 690 C (deposit on it) but may favor the 690 D if the feed back is more positive on the (1989) 690 D. I can see that the D Model is an improved hoe with higher pressure hydraulics and faster operating speeds. I owned a CAT 312 C and it was dream machine to run. I'm guessing that the 690 D is along the same line with the CAT 312 C and operates along that same level. I'm guessing that the 690 C is a little slower but still a fair machine. Anyway, tell me what you think. The 9XXX hour 690 D could be a real problem child. The 690 C may be the right machine, low hours, etc. . I need this hoe for about 6 months (500 hr.'s. use) and will re-sale it. Also, I'm opening the door to anyone that knows of another hoe for sale that's a older but a good machine, below $ 15 K. It needs to be within 250 miles of Huntingdon, PA 16652. Thank You, Avery