I've had to take out my AMD R9 290X while testing games on the R9 380 so I decided to give the waterblocks a clean. Over time, particles from the coolant/radiator/tubing used can get trapped in the microfins of the block and stick to the walls of the water channel. Maintenance is always a good thing to carry out periodically.
I won't bore you with all the details so I'll just bullet point the steps I took.
1. Remove the screws with a hex key (2 sizes of screws with this block)
2. Keep the rubber seals in a safe place.
3. Wash the block under a running tape and dry with a cloth.
4. Use 100% alcohol(isopropyl) to clean the internals and wipe with lint-free material
5. Put back together.

Next post will be on renewing the thermal paste.

Here's the PCB of the R9 290X. Every GPU has the same setup, consisting of
GPU core: like a CPU, it carries out the computations.
VRAM : acts a a buffer to store information used by the GPU core
Voltage Regulator Modules(VRM) : Provide power for the core and memory by transforming current and voltage. On the 290X these can supply over 200W, with an operating temperature limit of around 100 degree celsius. The 290X has 6+1 VRM's (6 on the right, 1 on the far left)
Power connectors: supply power from the power supply unit (PSU)

Back together again!