The crack itself (which is definitely a crack, not a glue seam) would not be so bad on its own,
but the presence of old glue in there is problematic for future repair. Furthermore, the white color
of the glue suggests "Gorilla"-type glue (most other common glues dry to clear or yellow/brown),
which is very difficult to contend with once cured.
If I had to fix this inexpensively, I would mix up a small pot of epoxy with some fine bubinga dust and
fill in the remainder of the crack. It would show, but likely would be stable enough.
Otherwise, it would take patient and careful application of heat and dental picks to get the old glue out.
(I have spent far too much of my life doing that already.)
The thumb mark above the pickup is typical for those (my '96 Thumb has it too)...it's just a by-product of the fact
that those Warwicks basically don't have a finish on them...the oil-wax blend is not a finish, really...just a polish.
It builds no meaningful film and thus doesn't protect the wood against any kind of abrasive wear.
Warwick depended on the hardness of the wood itself to keep it looking OK.
(Good call, too...finishing is the bane of most guitar builders' existences, and a huge cost driver for production shops.
I honestly think that one reason Warwick was able to build their impressive market share was by developing a
marketable product without a sprayed finish. I could cut my production cost by about 30% per instrument if I did that.
That means they had that much more money for advertising, artist relations, etc. etc. Smart Germans.)
Please note that this is NOT any kind of knock on Warwick - it took some guts to make that leap in the marketplace,
and I still own and love my '96 Thumb 4, which is a bass I will absolutely never sell.