spotlight mds segfault, mds_stores assert

Running Sierra 10.12.6 on a MBP Retina, 15inch late 2013).

I have searched everywhere, tried I think everything, but can't get spotlight indexing to stop crashing.

Mar 2 09:44:47 zv70 com.apple.xpc.launchd[1] (com.apple.metadata.mds.index[8306]): Service exited due to signal: Segmentation fault: 11 sent by exc handler[0]

and:

Mar 2 09:44:47 zv70 mds_stores[8329]: assertion failed: 16G1212: libxpc.dylib + 28737 [BF896DF0-D8E9-31A8-A4B3-01120BFEEE52]: 0xf

In Activity Monitor, I have looked at the crazy number of mdworker threads, then at their open files, trying to identify a possible bad file.

I purchased Norton Antivirus *just* to check that all files are ok (readable). This did actually fix a few files, but did not fix the issue.

I have monitored the size of the directory tree /.Spotlight-V100 using "du -s". It goes *very* slowly, then when the crash occurs, pretty clearly is all deleted.

I have restarted search using the preference-app approach (wow -- super-hokey, for years!) and:

mdutil -E /

I have removed all mdimporters in /Library/Spotlight (nothing in there now)

I have checked /System/Library/Spotlight and the mdimporters in there seem ok.

And

/usr/bin/mdimport -L

confirms what looks ok (only one MS Outlook importer).

In all of this, many system reboots (pretty much after every one of the steps above).

Any help on this would be really appreciated!

Seriously longing for days when I had Windows and X1 search.... it just worked.