Hi Kim, that's a common problem and a lot of people have 2 lids - 1 for desserts and 1 for savoury dishes. However in time the stain will fade but I understand how using a borrowed machine you are wanting to hand it back clean.
This from Quirky Jo's website although depending on where you live, there may not be a lot of sunshine around at the moment.
Quirky Cooking
2 August 2013 ·
{Top Tip!} Having trouble getting turmeric stains out of your Thermomix lid or seal? Here's a tip from a reader on Twitter: "Turmeric stain is unstable in sunlight. Leave things on the window ledge to degrade the colour." Thanks Martin!
I also find after a few washes the stain fades. (Then I go and do it again. Love turmeric