Looking for some advice again please folks.
I bought a second hand Skywatcher Skyliner 250 over the summer and got first light with it a few days ago. Very pleased with it, best views of Jupiter and Saturn I have ever had with a telescope. With a 10mm eyepiece, banding was clearly visible in Jupiter's atmosphere and I could clearly see Saturn's shadow on the rings. At one point, I thought the optics were fogging up but this turned out to be due to Jupiter just grazing the top of some trees in the next garden. While investigating the cause however, I shone a torch down the tube to check the primary and was horrified to see how dirty it looked. I checked it again in daylight the next day just to make sure it wasn't dew. If I look at it in natural daylight (as I did when inspecting it prior to purchase) it seems fine, but if I shine the torch at it the dirt is there. I took a couple of pics to illustrate this, see below:
I've read up on how to go about cleaning the mirror so I think I'm up to speed on that, but I have seen a lot of sources saying not to clean if it isn't necessary due to the potential risks associated with the process. Given the performance doesn't seem to be impaired, should I leave well alone or am I likely to see a big improvement if I do clean the mirror?
Thanks
Mike