laser 'arm' seems to be sticking about half-way?

On my Tevion DVD recorder, recording to about half-way through a new disk (at whatever quality setting, it seems) works ok, and so does play-back. However, beyond that and certainly on play-back, 'Error' constantly flashes up and the disk plays intermittently...with a lot of protesting by the machine at times. Attempting desperately now to archive my back-recordings by finalizing, I find that some do ok and then allow play-back, but some only appear to finalize ok but then refuse to play-back...result...loss of recorded material!!!

Changing brand of disk seems to make no difference, and the obvious step of cleaning the laser has made no difference either. Plusgas or WD40??? Any better ideas, please? Thanks!