Jrieves

I have a Series 2 (TCD240080) TiVo and a Series 2 DT TiVo. The DT TiVo works great with either of 3 remotes I have. The older Series 2 has intermittent problems with any remote. Sometimes I can press a button on the remote and the TiVo responds every time. Other times I must repeatedly press a key to get a response. The remote red light flashes but the TiVo does not respond. The front panel ribbon cable is firmly seated into the socket and I can see no obstacles blocking the line of sight.
Any ideas?
Is there a reference to a part number for the IR or to the IR circuit board in the front panel?
Thanks for any help, Jrieves