I wouldn't use any solvents or alcohols myself. That kind of stuff would probably dry the leather out and make it more susceptible to wear.
Leather is a remarkably 'forgiving' substance. I've taken leather jacket that was so old and dried out that it would just crack if you tried to bend it and brought it back into a useable condition. It was a sheepskin barn jacket that must have been completely water-soaked and just wadded up and thrown in a corner of a hot attic and left for years. I bought it for about 25 cents in a yard sale back in the early 70's thinking I'd cut it up and use the wool side as dye daubers. Just on a whim, I poured some cheap leather conditioner over it and let it sit overnight. The next morning it was supple enough to flatten out. I then worked some more leather conditioner into the jacket for about a half hour and let that sit for a few days. I took the jacket to a coin laundry place in town and threw it into a washing machine with a combination of laundry powder and dishwashing liquid and ran it through 2-3 cycles to get it clean. It really WAS pretty grotty! Yuck! I brought it home, hung it up outside but out of the sunlight, let it dry completely, then worked leather conditioner into the flesh side of the jacket again and let it soak in.
I wore that jacket for the next 15 years... Leather is a remarkably 'forgiving' substance. More so than my memory. I may have paid 30 cents for the jacket. It was a long, long time ago.

Stitchawl