I was thinking of checking my gearbox oil level (Felicia diesel with 117,000 on the clock) but having seen the number of people on here who've dropped the speedo drive into the box I'm not so sure. Is it a very common thing and what are the chances on a higher mileage car like this? I'm tempted to just leave it as it's running fine.

The reason I wanted to check is that there's a fair bit of oil on the underside of the box but then again it doesn't smell like gear oil - could be engine oil from the sump gasket on that end. I've no idea when or if the oil was last checked.

Risk losing the speedo drive into the box or risk running without gear oil?

I've never had it happen to me, and although I've only owned 4 felicia/favs to keep (3 rally, one road car), I've broken about 15, and removed the gearboxes from all of them (I had quite an appetite for synchros back in the day).

It's worth checking the oil, you should be able to get the drive out without too much trouble, and low oil will kill the gearbox sure as eggs.