Could well be selespeed fluid coming from the overflow on the resevoir. Very common when the accumulator one-way valve deteriorates and de-pressurises back into the resevoir - as it is not big enough to hold all the fluid from the accumulator (larger resevoir was fitted to later cars). If so don't really worry about it, just leave it to settle down and it should sort itself out when it reaches the right level. Worse than that is if it's coming from the gearbox. This could be due to the actuator leaking selespeed fluid into the gearbox and then being forced out of the output shaft oil seals, or input oil seal (over the clutch). This would mean that you should have needed to top up selespeed fluid before?
If its gear oil and selespeed fluid is ok and its coming from bell housing, then chances are that your input shaft bearing has broken up. This would also fit with the clunking of gear change. Solution: Box out, change bearing and seal - and probably clutch whilst you're at it.
It is easy to check the gear oil level - Fill / level plug on side of gearbox (i.e to front of car). If it is overfull, then its probably selespeed fluid.
If fluid is from overflow, then clunking may just mean that you need a end of line reset on gearbox and adjustment of clutch plunger length.