Keychain is not updating passwords properly

When I log into many web accounts where a password is required the password offered in the login box is wrong. This can only be discovered when you accept it and the web site rejects the log-on. Fortunately I keep a written (yes pencilled on a card index!!!) index of web sites and log-on details. Checking the current passwords against the Keychain version the latter is clearly wrong. If I try to correct this by typing the right password into the web logon and hitting the Save button when asked of i want to update the keychain it fails - the keychain still has the old password.

This is particularly annoying with often used passwords. For example the Apple ID password isn't correct and this triggers an update action where the two step validation kicks in and I am asked the laughable questions "do you trust this computer" and "do you trust this browser" - they haven't changed!

Looking at past posts (now closed) the fixes offered do not appear to apply to High Sierra - Keychain First Aid is no longer available. What can I do to correct this please? I attach a screen shot of the Keychain folder - can I simply delete the folder contents and let the machine rebuild?

The Keychain is shared across an iMac, MacBook Pro and two iPads.