Theoretically, if your servo is not cracked, you can bypass only the inlet side and leave the outlet side connected thru the servo. I think that is how ************** sells their kit. Test it.
However, if your servo is not rusted in a stuck position inside (interior leaks happen also, not visible as external leaks), you might later consider bypassing the outlet side in order to save the possibley working servo mechanics/electronics from future leaks and rust.. That way you can keep the amp installed and maybe revive your A/C.

Just back flush yourself instead of hiring.

buy a garden hose attachement to stick into the open heater hose (use a hose clamp if needed, then detach the outlet side hose and divert it into a bucket.
Attach garden hose and flush away.
you gain by knowing the actual 'before and after' condition. flush until clean.
use store bought water and a good antifreeze like MBZ coolant for refill.
Flush or drain your radiator while u r at it. easy.
top off via the top radiator hose to prevent air bubbles.
not hard. just get organized and take your time.

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1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
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1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD