I had a problem with a PK6 gearbok on my Laguna. Just before I bought it, the clutch was replaced due to oil leaking from the pump. All well, and I've been driving it for 3 years or so. Lately, I've noticed that the gear changing has been sluggish at best. Especially 2nd and 3rd, but also had problems putting it in 1st. I suspected a leak from the driveshaft oil seal, so I ordered that, together with the correct gear oil, Tranself NFP.
But as we where going on holiday, I didn't have time to replace the seal, but I thought I'd check the oil level. Off the wheel and the trim to get to the filler screw. Renault documentation say you can make a dip stick, and I did that. Checked oil level first and found it too high. As it is a bit tight in there, I checked it again. Put the stick back in, and lost it
My pulse skyrocketed and all sorts of scenarios went though my head, pulling the gearbox and all. But after I calmed down, I found a flash light to look inside the hole. And low and behold, I saw the stick and managed to pull it out with a pair of pliers. Day saved.
End of story is that the guys that replaced the clutch did as they normally would, fill the gearbox to the rim with ordinary gear oil. So I had way too much in mine. Drained the box of about 4 liters and filled it with 2.2 liters of NFP. Now if feels like new again. Like butter. So it's definitively worth getting the correct oil and level on the PK6.