A lull in this thread made me think that everyone had disposed of it two days ago, but there has been a flurry of activity since then.
For anyone still battling with 12d, it's not all that hard provided 15a has been filled, and preferably 18a as well (not many options there). 2d can be worked out by considering the clues for 5a and 7a, and the possible answers for 8d. Once you have an answer for 2d you will be able to work out how many seconds the snail takes to travel 1 foot. That figure must be a factor of 12d, which gives three options for that entry, only one of which ties in with 1d.
People have mentioned the greedy cat and the speedy snail. What about the randy Master? Or is he a Catholic?
S_pugh, your tally of even numbers is correct, unless I've also made an error.