[Tenfc]

I am new here, and know very little about cars.
My mother has a 1999 Olds 88 -3.8Ltre engine. 80k miles.
4 months ago her car broke down and the repair shop said her coolant was leaking into the engine oil. They made the repairs replacing gaskets and I think the 'intake manifold'? The engine coolant was completely dry and apparrantly the engine had a gallon of fluid in it..(coolant plus oil)
She spent the $1300 bucks for the repair.
Now, 3 1/2 months later the exact same thing happened.
A repair shop told her this is a common thing to happen with this make, model, engine and year. They said they see about 10 a year with this problem.
I know very little about cars, My mother is older, and lives a few hours away from me. Is there anyone who may be able to confirm this information or have any suggestions we can explore? I haven't been able to find any info elsewhere on the internet. Any comments appreciated. Thank you.