Not go too far with this.

Stuck trying to get Holmes to look at his newspaper collection, after having looked at the ring in the evidence tray at Scotland Yard.

Every time I try and interrogate Neligan to get the Q symbol re the ring Nelligan just proclaims his innocence.

Having checked the walkthrough I think I have done everything including the harpooning experiment.

Help anyone?

You're right - the usual problem here is the ring.
Redo that part:
Go to evidence room again and look close at Neligan's ring.
Read the inside inscription and turn it all.
You have to see and Holmes to know the complete writing - from R Dawson to my friend and partner, 1883. Rotate to view all the inscription.
Start at beginning, move the ring, read the next part until all the inscription is read.

Thanks MaG. It was the ring. I thought I had already thoroughly examined it. Didn't realise there were 3 points of observation for the inscription!

Wonderful. Have fun now!