TV remotes the most common cause of that film is the use of furniture polish in a can near the remote, which then accumulates in the unit. Done quite a few with cleaning with methylated spirits, and in many cases that, along with resoldering the IR led, the capacitor ( or adding a small capacitor that will fit in the case, typically I use a salvaged 6V3 470uF capacitor from old computer motherboards, choosing those that have not bulged and which have low ESR under 1R) and the 455kHz resonator, glueing down if loose with a small drop of superglue, and finally resolder battery springs and clean them up.
New batteries if the old ones are close to expiry ( though some had Duracell batteries 10 years old in them, still doing fine so left them) and close up the unit again. Some needed the case welded together to hold the battery door in because of broken plastic, so changing batteries is a service operation now.