What clutch to replace them with is like having a "Which anchor is best" conversation. We have the Lewmar D2's and like them - almost no slip when engaging under heavy load and easy to open under heavy load. I also like the fact that they open towards you. Anyway, practical sailor did clutch reviews recently so you might want to look up that article. I'm surprised to hear Garhauer doesn't have replacement parts for those ones...
You can get nearly identical Garhauer clutches from Catalina Direct. It looks like you have four singles there, but you could do two doubles or a triple and a single to get all four lines covered. These clutches look like something out of a tractor factory but they are affordable, strong and durable.
Regarding singles vs. doubles vs. triples... We have Lewmar D2's which have to be sized for the line going through them (usually allows a 3mm variance in line size). I don't know if all clutches are like that or not, but with singles you can replace individual clutches if you change line sizes. We just did that a few months ago when we ran a third reef and had to swap out two clutches. Using the singles, we could just swap out the two and not have to swap out the entire bank. I know you can just replace the innards, but it only took me about 3 minutes per clutch to unscrew the old one and screw in the new one.
IMHO, the best line clutches are the Lewmars. The mechanism they use is the easiest to adjust under even the heaviest load and does the least damage to the lines. Spinlocks can often jam under high loads, requiring you to ease the load on them using a winch prior to releasing them. They are also among the least expensive of all the line clutches.
However, Lewmars, due to the "domino line clutch mechanism" they use, have the smallest range of line sizes they can handle, and need to be sized appropriately for the task.
Be aware that the Lewmar line clutches open in reverse compared to many other brands... and note the little winch icon and arrow on the line clutch when installing them.