Hello JDP and others interested in vintage recorders.The problem with the Uher 4000 speed {And also other old Tape recorders} is most likely that the belts are quite worn and need replacing. Also it has a couple of other rubber parts which get worn out.These machines are quite old now 35 to 40 yrs.To be working at all is amazing.Belts may be obtained from
www.elektro-ersatzteile.org .I think it is a German company. Havent bought anything myself but they do say they have belts for Uher and other mainly european. The belts on the Uher arent too difficult to change but there is a knack to it.. Hope this is of help...... Reelguy . Ps If the address doesnt work try, Eberhard Hewicker in the search bar its the same place