Worth calibrating a Di-Log tester?

I forgot I had a Di-Log 9803P so called '17th Edition Tester!?', it was a rash ebay purchase a long while ago intended as a spare, and I discarded it when I thought it didn't have a high-current loop test. In fact there is a convoluted way of doing this but it wasn't in the original manual. An update was later published describing it. Anyway...it's sat in a cupboard for about 2 years.
I've just found it again and it appears to be out of calibration to a degree I've never seen before. Test leads are measuring 0 ohms so nothing to null.
Two trusted testers (one of them recently calibrated) are giving me a high-current Zs test of 0.21-0.22 ohms on an installation. The Di-Log is consistently giving me 0.11 ohms (high current test). It's obviously reading very low, but for a micro-processor controlled tester it's a long way out. IR tests seem about right and RCD testing seems ok.
Any opinions on whether it's worth spending cash on getting this calibrated? It if came back calibrated ok I'd probably keep it as a spare.
Very long shot but if anyone has a service manual for one I'd appreciate it. (I can offer a service manual for a Megger 1500 in return!)
Thanks for any advice, especially if anyone is actively using one of these, or had one go way out of calibration.

Unrelated - thought some might like to see the trusty old analogue loop tester continuing to behave in a rock solid manner:

and it's never far wrong:

Do you have the original leads for it?

I ask because I have a DiLOG 9118 and wondered at the low ohms lead-nulling not seeming to impact on the Zs results so I asked them how the cable's resistance is corrected for and they told me it was a fixed calibrations.

Having 0.1 ohm of a difference in probes between assumed and used could explain it, but I have no idea if you get it calibrated if they would do that with the leads you use (i.e. adjust out both meter and probes in the one go) or simply to a factory default for the probes the assume you use.

Sadly none of the MFT offer 4-lead Kelvin connections to make that all automatic and more accurate

Thanks for reply. I was also wondering about the leads.
I have the original 3 probe to 3 pin plug lead and the original fixed probe, but the rest are all Kyoritsu leads and probes/clips.
Di-Log say that the LS3W907 lead set is compatible with the 9803P, and in fact several other testers including Kewtech, Fluke and Megger. This suggests the leads are reasonably interchangeable.

Another little test, a 10 ohm resistor (lowest I could find) on a calibrated BM400/3 (with leads nulled) and the Di-Log. Both have new batteries.
I guess the only way to be sure is send it off and see if it can be bought into calibration.

I then thought of using an alarm fuse:


An 100 ohm resistor then gave 98 ohms on Di-Log and 99.9 ohms on the BM400
So there seems to be proportional drift, ending up about 2 ohms out. (The BM400 range ends at 100 ohms.)
Calibration time, if I don't try it once I'll always be wondering if it might be ok.