Wood stain in stairs

[4rchibald]

What would be your suggestion to stain old stairs that are sightly discoloured due to sun, incomplete varnishing (as you can see, the middle strip was not painted) and few joint pieces of wood as shown on photos.
I have tried Mann's water stain but I'm not impressed with the result (smallest remain of old paint can't be covered) and it looks green-gray colour.
What would be your suggestion to cover those imperfections with a light oak colour and overcoat with varnish

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[oldcardriver]

There used to be a brown brush paint on the market that produced the appearance of light streaks in the painted item, like a wood effect, but I can't remember any more than that.