Many apologies, I meant 39a, not 36a! To reiterate, my 39a and 25d only have one letter in common, but that letter also has to go at the intersection of 39a and 37d.Thanks to those who replied, I’m very confident of all three solutions!
I am finding the end game rather frustrating. I believe there are 5 related elements, described by the first word from the correct and omitted letters, which are to be highlighted in the final grid. Three of them are readily identified, but the other two (3 and 10 letters respectively) are not to be found.
0pt0 - the 3-letter element you have to supply yourself. To find the 10-letter element I scoured the grid for occurrences of its 7th letter and found it that way.