Oncidium leaves turning translucent. Virus or sunburn?

[Evil Gnome]

Hello friendly folks,

Long time stalker here, I decided to post this question as I became slightly worried about my oncidium lately - it had a rather ridiculous amount of aphids on it a while ago that I managed to get rid of using pesticides however it has now developed a translucent patch on one of the leaves and it leaves (no pun intended) me worried that it might be something more serious.

The plant is situated on a southern facing windowsill - temperatures are quite mild most of the time as we don't get too much hot weather in Scotland however there were a couple of really sunny days recently so it might have gotten a bit too much exposure. I water weekly, together with my phals by submerging it into a tub of room-temp water for 20-30 mins and letting it drip before putting the plants back into the glass outside pots - I check a few times afterwards so the plants don't sit in water.

Being a real newbie to orchids I will assume user error before anything however I thought I'd ask here just in case it's something I can remedy.

I attached the photo - the affected leaf is the one on the right.

Many thanks in advance.