The 993 has two plastic undertrays which protect engine and gearbox. They are held on with only a few screws / clips and are very quick and easy to remove. With the undertrays in place, it's almost impossible to see if there are any oil leaks - any drips collect on the tray - not under the car on the drive / street so no oil on the pavement doesn't necessarily mean no oil leaking!
Plastic Undertrays in place
Once the undertrays are off, you can inspect the engine and gearbox properly to see what's going on. Typical 993 areas where oil can weep is from the cam covers, chain covers and gearbox seal. It is very common for these areas to show signs of leaking. Damp is nothing to worry about - worth changing when having other work done but not essential. Major leaks = engine out = big bill.
Undertrays removed - engine and gearbox guts exposed
It was great to get the car up on a ramp and have a good look underneath. Not often you see 3 993's in a row at an OPC these days...