I would try washing it.
Remove action/barrel from stock ,remove bolt, remove trigger if possible. Use a reasonable detergent, warm water and wash the rifle. Pay attention to nooks and crannies with a toothbrush Rinse well with warm water. Rinse with very hot or boiling water.
Dry it quickly then oil everything. Remember the bore.
Later clean off all the oil possible by blowing with compressed air. wiping, whatever it takes.
Then wax everything with a quality paste wax.
