Just for information rather suggestions upon your beast.
Several of the Power Mac G5 range have liquid cooling, including my Quad-core. It does seem to work well. However, once breached the salvage appears untenable.
Failures are rare but I have a friend with an early G5 which was bought 2nd hand and may have had internal physical damage and has leaked, it will run for a decreasing time before dropping out. Now at 12 minutes.
Quotes for a fix are more than a current 2nd user high spec. unit from a reputable dealer.
So liquid cooling is very useful but sound plumbing is necessary.