To address this, I use a water-based degreaser inside and out. The exterior gets a good scrubbing with a cleaning pad, but the interior is more of a challenge. For this I use a flexible baby bottle brush from the dollar store with a strong solution of degreaser and hot water. Keep at it, and you'll soon have it looking its best.
If those stickers have lost their sticky, a little rubber cement or all-purpose glue will put them back in place.