So yes, dichroic filters can indeed lose efficiency over time, and often do, due to either bits of coating spalling off (excess heat), or gradual grime build up inside a colorhead as less than ideal gasket, paint, or diffusion materials slowly decompose. Big commercial color enlargers are designed to tolerate higher internal heat levels than amateur enlargers; but if the needed light output level was high enough, their dichroic filters and reflectors needed to be periodically replaced. If you do open up an older colorhead to inspect and clean filters, just realize that old coatings can be quite fragile, and must be cleaned with extreme care.
An Omega D3 does NOT have a high-output characteristics running hot enough to worry about as long as the fan is working. It's still a good idea to inspect the general condition of the filters, and to make sure the mixing box hasn't yellowed. But if the filters look bad, it would probably be cheaper and easier to replace the entire colorhead than just the filters themselves. Full units, chassis and all, sell for relatively little these days.