You can easily go 10k + miles on intervals. Don't waste your money on cutting them in half. Plenty of UOAs out there to support that as well.
As for your seeping transmission, manual gearbox? Mine was the same, just seeping a bit and collecting dirt making it not look very new. I have had mine off to upgrade clutch and add a limited slip diff, so was able to reseal the case and have been leak free and clean underneath for 10k miles
If that's the case for yours, good luck getting the dealer to fix it as it's likely not bad enough to warrant a fix. But, you'll want to have some spare fluid on hand to top off possibly. It's ~$12/liter I believe for the latest flavor. Part# G052512A2