Gearbox Oil Change
The challenge lays not in removing oil but putting it in. The transmission is filled through the hole where the speedometer drive cable enters the housing. The first job is to remove the Speedometer Cable and speedometer gear from the gearbox and remove the speedometer gear to check the oil level. Please do this before draining the old lubricant. If you're not able to remove the cable, it's better to find out while there's still oil in the transmission.
If you need to add or refill oil you’ll need a funnel and suitable length of hose (nobody said this was easy). The original Mobil oil specified by Lotus is no longer produced. Lotus next recommended Castrol TAF-X 75W-90. TAF-X 75W-90 is no longer available but has been replaced with another Castrol product (see below). Draining the gearbox is simply a case of removing the transmission drain plug from beneath the car. The LEC how-to section includes an article with photographs.
Capacity and recommended lubricant
Lotus manuals state 1.8l / 1.9 US quarts as capacity for refilling a drained transaxle. 1.9 US quarts = 1.8l = 3 imperial pints = 60.8 fl oz.
Recommended lubricant is discussed at length in this forum thread and this one. Castrol TAF-X 75w90 originally recommended by Lotus is discontinued. As of 2011, it is replaced by Castrol Syntrans 75W-90 in the UK, Syntrax 75w-90 in the US. Redline MT-90 (not MTL) also meets these requirements. For those who have installed Quaife differentials, they also recommend 75W-90 synthetic gear oil.
Bottom line: 75W-90 GL-4 full synthetic gear oil.
The mysterious refill plug
Some may have one. Some may not. Read on!