Just giving this thread a bit of thought, especially with the Autumn months ready to fall upon us.
Checkout Jules shop for his own design Plenum Guard. It's a great bit of kit, no leaves can pass it and it looks like it was a OEM fitting.
The picture shows a drain plug in the position that you would expect a grommet to be fitted to, even though very little water actually runs though it, I feel it's better to be in place.
