Is the turning error increasing linearly or lograthmically(or something!) as you turn from West to North (northern Hemisphere)? Only once had a DI fail on me and sort of continued on VOR to desination and then tuned in ILS in dodgy weather.No problem but timed turns(or at least for the final correction) would be my preference. Some compasses are not as damped as they should be and the value of turning error is varying madly in turbulence which all adds to the problem.
I prefer Compass 'lags'and becomes 'sluggish' as you turn North and 'races ahead'and becomes 'lively' as you turn South ( too lively at times- swings back and forth so the timed turn is probably better on Southerly headings.
I have I got anything wrong? - quite prepared to be corrected.