2012 VTX Circulation Pump Question

[SpartanVTX]

I have a 2012 VTX with a Monsoon 350. I’ve been having temperature fluctuations while at speed for a while now. At speed, the temps are about 175-190, but the temp drops down to a cool 160-ish as soon as I return to idle. I’ve found the posts regarding the service bulletin from Indmar regarding the circulation pump on the forums here. My engine serial number is about 800 engines before the supposedly effectived circulation pumps. Ultimately, I am fairly certain that I’ve narrowed my high temp fluctuation issue to my circulation pump. Especially, since in addition to the temp fluctuations, my heater doesn’t seem to actually be pumping any warm water through the system (no leaks and I can blow water through it) and it is of course connected to the circulation pump. 
 

That all said, I can’t seem to easily find the circulation pump part number in the aforementioned service bulletin (551045SB). I can only find the circ pump with part number 551045. They appear to be nearly identical, except that 551045SB does *not* appear to have the water bypass hole on the left leg of the pump. The question is, does anyone know if these pumps are actually compatible? The engine block *appears* to have a corresponding hole for the bypass hole on the pump, but…admittedly I don’t know nearly enough about this sort of stuff yet and don’t want to create a bigger problem. I just hope I don’t need to continue to scour the internet for this mythical circ pump without a bypass hole

Thanks in advance for any assistance.