Cessna 172 climbs to avoid glider during IFR descent near cloud base

A Cessna 172 R on an IFR training flight came within an estimated 40-60 m of an unidentified glider near Bergheim (Germany); the Cessna landed safely. The Cessna was in IMC descending toward 915 m AMSL with the instructor flying while the student configured the avionics. During a frequency change the student saw the glider through a cloud veil, slightly below and turning toward the Cessna from the left. The instructor terminated the descent, climbed and turned right, and levelled at about 1,280 m AMSL once clear. The glider, marked with red tape on nose and wingtips, was flying without a transponder and could not be identified.

1. IFR training descent toward MGL: A Cessna 172 R was on an IFR training flight from Cologne-Bonn to Mönchengladbach on Langen Radar frequency, with an instructor flying and a PPL student configuring the avionics. After clearances down to 4,000 ft then 3,000 ft AMSL (~915 m) and a frequency change instruction at 16:26:10 LT, the Cessna was on a northbound heading.
2. Cessna in IMC, glider below cloud: According to the instructor the Cessna was in instrument meteorological conditions during the descent. The glider was operating below the cloud layer in marginal visual conditions with cloud and haze; METAR Nörvenich reported few clouds based at 3,500 ft AGL and scattered at FL70, surface visibility >10 km.
3. Glider without transponder: The unidentified glider was flying without an active transponder, so it did not appear on civilian ATC radar. Military primary radar later showed a primary target about 0.4 NM south-east of the Cessna at 16:27 LT moving north-east. The glider could not be identified after the event.
4. Student spots glider via cloud veil: During the frequency change at about 16:27 LT the student noticed movement in his left peripheral vision while inputting nav data. Through the cloud veil he saw a glider slightly below and turning toward the descending Cessna from the left; with the Cessna still descending the two were on a converging course.
5. Climb + right turn: The instructor terminated the descent at about 3,900 ft AMSL (~1,190 m), initiated a climb and right turn, and levelled at about 4,200 ft AMSL (~1,280 m) once the student reported clear of the glider. The instructor saw red tape on the glider's nose, after which the glider turned left and the red tape on its wingtips became visible.
6. Pass ~40-60 m, Cessna lands MGL: The Cessna pilot estimated the lateral separation at the closest point as about 40 to 60 m. There were no injuries and no damage. The Cessna landed normally at Mönchengladbach.