Video detailing the transmission removal process. I originally thought the dual-mass flywheel had failed, as the symptoms were indicative of this, but upon removal of the transmission discovered I would be needing a new transmission.
Rather than replace with another 5-speed, I decided to replace the transmission with the 6-speed transmission used in GTIs and GLIs. The 6-speed is much stronger and more reliable, and also much easier to find, as many more people buy manual GTIs than manual Golfs in the US. This video outlines the steps I took to integrate the new transmission.