greedy kite
I think part of the problem, at least for me, in 'seeing' the 17s is because solving on-line we only see the 'P' once - we only see 11 letters but there are 12 in the answer - whereas if you write the 12 letter answer down it's clearer.
The first 6 letters are the a car maker (4 letters) and 'op' all reversed. Then the last 6 letters of 17d.
I have an answer for 20d but I'm not too keen on the definition - there are 2 cars I can think of but only one of them can be a 'bee' - I think. Assuming a noise a 'bee' might make. Any thoughts?