I have a Paterson PCS 2500, which as best I can tell, is identical to a Philips PCS 130. These enlargers are no longer made and are hard to find parts for. You might see if you can buy another one (mine came with a very full complement of accessories--3 condenser sets, several neg masks in addition to the glass carrier, and a few other goodies--for around $200) and just use one for parts, or just get another, more common enlarger like a Beseler 23C or Omega D2 to replace the Philips.

Also, be sure you are inserting the filter holder correctly. The design is a little cryptic. The way it should work is that the panel below it that covers the condenser box is sprung. You have to push in that panel to grab the lip under the filter drawer that lets you pull it out. When you push in the drawer, be sure it goes all the way. If it's just bent, it shouldn't be too hard to straighten. Also, if you have the metal frame inside the drawer that holds a piece of heat absorbant glass, be sure that it isn't bent. The fit should be fairly tight. It's a well-designed enlarger with really no light leakage. Philips enlargers were considered to be really fancy in their day.

Not as convenient, but yet another option is to switch to under-the-lens filters, but for a public darkroom, this may not be such a good option, because it is harder to keep them clean in that situation.

Used darkroom equipment is cheap these days.