Rotary hammer only rotates when held vertically

• Very inexpensive (i.e. cheap) rotary hammer, ~ 20 years old
• Only rotates when held vertically. As soon as it is tilted slightly, it stops. When it turns, it drills without any problems, even with hammer.
• The problem has worsened considerably in a few weeks, now it hardly starts at all.
• The carbon brushes still look good, but I have changed them anyway - no change.

Is there any hope for the hammer drill?