Not unusual at all.
Whilst not for Watercooling AIO's, I am RMA'ing a set of RAM back to them right now. Taken over 10 days so far, but technically they have been updating and responding to me (after I gave them a tiny bit of space before updating my ticket and needing them to respond).
A quick rough timeline:
~11 days ago: Submitted request for RMA.
~10 days ago: Ticket was created for me.
~10 days ago: I updated Ticket with image of Invoice, etc of order.
~9 days ago: RMA Ticket approved
~9 days ago: Clarification on RMA and what to send requested
~8 days ago: Clarification given by Corsair
~8 days ago: Sent RAM back via Special Delivery Royal Mail
~5 days ago: RAM arrives at Warehouse
~3 days ago: Updates ticket on arrival, giving details
~3 days ago: Corsair updates me with available replacement options:
~1 day ago: After questions on replacment and options given, have selected a replacement option that is now underway by Corsair. Will be sent tracking for replacement via DPD after it has been sent. 1-3 days projected time (I'm guessing Work Days). Expecting arrival by next Wed.
Most of it was spent on communicating with the Customer Service reps, otherwise it was fairly quick. But yeah, approaching 2 weeks turnaround at the moment. Although a few days were wasted on clarification as the reps were giving vague one sentence answers to questions that needed more clarification.
