newbie question: sythetic to regular oil
 

Good morning Forum!
Just joined, first post. I'm sure my question has been flogged to death, but...
My son has a 2010 Cooper. He loves it...but so far he's changes the timing chain and just replaced the clutch yesterday. Afterward the shop couldn't start the, spend about 7 hours figuring it out, no definitive reason why? Did a whole bunch of checks, including a compression check, which was low. we got into conversation about next steps, clearly an engine rebuild is out of the question. It drinks oil for fun, I guess now we know why! So, instead of putting in a litre a week of synthetic, I was hoping to switch to conventional to save him some money and change it more frequently. So, I'm wondering if anybody has any advice or history with this type of issue?
Thanks so mush for your time!
Scott