You might have a look at the knive. If it it does not look sharp, might take it out and try to resharpen it. But due to its serrated form you need special tools. Do not attempt it unless you successfully did similar work before.

Alternatively you might try the Agfa Rondix 35. It is a daylight-loading tank of more simple design and without reel. The film is not cut off.

The most recent model of a daylight-loading tank comes from Jobo and was marketed until few years ago. It is based on the 1500 tank system.