Yes, I saved the ECU from a soaking, just in time! The plenum, or scuttle drains on a Rover 75/MG ZT are a VERY common issue. They get clogged, water collects and eventually soaks the ECU. Undesirable. It also soaks the cabin filter, so that was replaced at the same time.
Much of the info was gleaned from the incredibly helpful Rover 75 and MG ZT Owners' Club. https://the75andztclub.co.uk/
Lovely HubNut goodies [including 2021 Calendars!] can be purchased at https://hubnut.org where you'll also find support options.
Or, support HubNut at https://patreon.com/hubnut or via Channel memberships: https://www.youtube.com/channel/UCfxlBQnvNXX6o-2KbCMszWQ/join
Don't forget to like the video if you like it, and share with your friends if you really like it! Thank you all.