The other thing is that we know what was sabotaged was the Keeper's ability to receive the signal, meaning had they ever actually checked on the Citadel itself they wouldn't even have needed anything special to figure out what happened because it simply would have just worked. Whatever button the Keeper's used Saren could have just pressed to summon himself up some Reapers.
Not to mention that the conduit is just a relay to the Presidium. Shep is right behind Saren at that point and Saren never talked to Vigil(who is the only reason we as players know what happened), so he didn't have the time to study any sort of notes one can argue he might have found on Ilos.
It doesn't tell them anything beyond the Protheans got back to the Citadel and sabotaged something, which is information they already knew. After that failed they clearly went to manual activation mode based on no new additional data gained from finding the conduit, so why didn't they just make that plan A?
and that's all assuming they can't scan anything, which is itself not an absurd notion considering a Salarian/Volus duo was able to scrape enough together to figure out something isn't right with the Citadel. Reaper tech should have been miles ahead of Chorban, doubly so because they genetically engineered the Keepers.
But we don't know how the Keepers open the relay. We don't know if the controls are accessible to Saren, or if he is even physically capable of activating whatever controls were used. All we know is Sovereign has to access the Citadel personally
A weak point, I admit.
Remember, Shepard went back to the Citadel, reported to the Council, had the Normandy put on lockdown, met with Anderson, and escaped from the Citadel before going to Ilos. Whereas Saren could simply go straight there. Saren had a head start of hours, if not days. Plenty of time to find notes. Especially given he had the Cipher too.
Once they found it was the Keepers that were sabotaged (remember, it took decades for the Protheans to find a way to do this, likely lots of notes to be found there) , perhaps they decided the direct confrontation was the next best option. Even if the Keepers could be repaired enough to open the relay, at this point Saren was exposed and couldn't possibly do it.
Chorban didn't discover something wrong with the Citadel, he discovered that the Keepers were supposed to react to "something" every fifty thousand years or so. Sovereign would go "Well DUH!" at that. That the Keepers were bioengineered was discovered later, when Chorban got a look at pieces of Sovereign.