Help with EPDM flat roof recovery

Carport that an amateur (me) applied .45 EPDM over/adhered to OSB approx 8 years ago. … .I know now bad move

Didnt take long to start leaking. Had to make 3 seams (at the time) for installation. Transition to shingled gable is also a probable trouble spot.

Have reseamed a couple times. Still cant get it stop leaking.

Plan:

Have purchased .60 EPDM sheet —Now able to purchase 1 single piece 20 x 40 to eliminate the seam issue. Transitioning to the shingled gable still tricky but will be hiring experienced roofer on his off time to assist.

Have a couple soft spots, especially at gable shingle transition and a couple small other spots where ponding occured. Figure I can hack those
out and replace with new plywood prior to re roof.

Am I on the right track here? Internet research shows I can use a RECOVERY board type of polyisoboard to cover old and re-lay new .60
over top assuming substrated is still solid and or I repaired soft spots.

Owens Corning makes a durapink Iso board specifically made for Recovery roofing. Do I really need recovery board? Is it that much different then regular isoboard? Willing to spend/go the extra mile here not to have to
go through another tear-off…
There is very little if any pitch to this roof. Assuming the substrate is solid, would I be able to start at the gable shingle transition and “step down” some plywood i.e 3/4 to 1/2 to 1/4 inch plywood to create a pitch? As above the recovery board would be applied on top of the plywood then the new EPDM.

Appreciate all ideas and replies…

Use Polyiso taper to get the water off of the roof. If you leave the old EPDM on the roof, cut it up so it does not cause moisture between the new and old roof. If you put the last system directly over plywood it has no fire rating…

Thank you donl for your reply after so many views… After your advice I researched polyiso taper board (thank you) . Seems like most info I find is more geared to commercial roofing applications which I am sure you are the professional on.
As before this is a small (20 x 40) diy project. I would love to find polyiso taper board but I am having a hard enough time coming up with needed materials to do this job due to the fact all roofing suppliers around here wont sell to me because I am not a roofer with license( rightfully so). I am going to ask the local big box store if they can specifically order me Owens Corning Durapink Iso recovery board as they carry Foamular iso board version for siding/vertical applications. Any other advice you can give me would be appreciated,

Thanks again!

The roofing suppliers will usually sell to anyone, even though the sign by the door says otherwise.

Do you have a ABC supply in your area?

Yes Axiom

20 Mile from here but I will check with them. Thanks for your recommendation

Nukklehead

A salesman at ABC will be able to help you with everything you need for your project.