I am not a fan of Lumiweld or any of the similar products either.
Most of them are just a zinc based alloy, which s why they are a darker colour , a lot more bluer.
In sub critical places like a chaincase where the foot peg has gone through, fine but on the oil pump mount, you are dancing with the devil.
The thermal expansion of all of these alloys is nothing like that of aluminium - silicon alloy that the cases are made from.
Secondly it does not adhere to dirty metal which is why when the demonstrator is showing off the stuff, they usually blow a hole in the casting so it has a nice clean surface then proceed to fill the hole with the Lumiweld
Most of them are around 5% Al where there is a eutetic point as seen in this diagram
https://www.researchgate.net/figure/The-Zn-Al-equilibrium-phase-diagram-26-The-vertical-thin-line-represents-the_fig5_239521389 Compositions either side of that point will be workable ( mushy ) for a short period before they solidify which is where you are working by scraping the surface under the "weld" puddle with the stainless brush or titanium scraper to break up the oxide layer on the parent metal. It is thermodynamically similar to lead wiping and chemically not too far off either.
Note this diagram is simplified to a binary one and remember you are trying to repair an Al-Si or Al-Si-Cu alloy not pure Al.
Zn & Si do not alloy so the Zn has to disolve ( like sugar in your tea ) into the Al ( Alpha phase ) in the casting and push the Si out of the way.
The Si accumulates in the grain boundary regions making the repair very stiff & quite brittle.
For a region such as under the oil pump, real welding is the only option and I would go with torch welding rather than electric welding.
Been a long while since I have been playing in this region but from memory there are some cross drillings that run very close to the mounting stud holes & I fear that you may have breached one of them so now the helicoil is out have a very close look at the hole with your new magnifiers .
Good luck