Repair around window frame

The plastering around the double glazing in the house we bought was horrendous and out of warranty. The plaster wasn't level with the existing plaster and they had even plastered over the wall paper. I dug out the plaster around the window frame which revealed that they just filled everything in with browning plaster.

I was advised to internally put sealant between the birks and frame. Fill with a strong mortar mix 4:1 up to the current mortar level then base plaster and skim. I followed this advise on one window but I get damp patches in the bottom corners of the window.

From the attached pic you can see that some of the external bricks sit inside of the frame, then there is a damp proof layer. I think that the external brickwork is getting damp in bad weather and moisture seeping though to the plaster.

How do I fix this? What the usual method of preventing moisture seeping through? Is there a way that I can waterproof the external bricks before applying the mortar layer?

the position of the window jamb, relative to the inner and outer leaves of masonry, is incorrect.

the window should be covering the dpm join between inner and outer leaves of masonry.

OK, as I thought moisture is seeping into the plaster work. How can I fix it without refitting every window in the house?

I was thinking of some sort of adhesive to hold a damp proof layer onto the brickwork, then repairing as per the original post. Would this work?

Any other suggestions?

Thanks for the advice. I am going to tidy up the masonry between the DPM and the frame then cover with a liquid membrane to waterproof the brick work.