Redline MTL (GL4) works very well in the type 9 box,
Additives such as the ones listed above should be avoided as they can be counter productive by being too slippy which impairs gearchanges, encourages excess pressure to be used and leads to premature wear and breakages.
Oh dear "Too Slippy"
2019 310S 1.6 Sigma
OP, Neil is spot on, don't add any snake oil to a decent GL4. It's totally unnecessary and can cause problems.
If you have a decent GL4 in there and still have an issue it isn't going to be solved by any additive, let alone Slick 50, the ultimate snake oil.
I'm surprised they're still going since the lawsuits of the 90s, the power of advertising I guess.
Have you tried adjusting the selector locking spring pressure?
OK, where is it? It's socket head screw about 10mm diameter, at the front L/H side, at the top of the maincase, if this is to far in it applies excess pressure, via the spring, to the locking pin behind, which then binds in the gear selector shaft detents, causing poor gearshift action.
Presently this screw on my 'box is about flush with the gearcase face. If you change this, you may have to apply some new thread sealer to the screw to stop any leaking, how do I know this?
Hope you can get your problem sorted without having to remove and dismantle the gearbox.
Can't beat good old 'cooking' Halfords 80w-90 GL4. Used in three cars including the R400 & cannot complain. I do change at the ten year point which in the case of the latest car will be at about 25,000 miles when it comes around.
Beware of additives. If they were required then OE manufacturers would either recommend them, which they do not, or as in most cases the oil already has friction additives of some sort as part of the recipe.
Choice of oil make/type is all down to personal preference & of course the recommendations given.
I think the easiest option to evacuate the oil is with the lid off and a pela pump. Lots of fumbling down the tunnel from the engine bay!
If the box has to come out ask about getting a drain plug fitted. I'm sure I read one of the specialists fits them in the ally bit between the main case and tail. Also look at getting a filler / level plug in the lid (Quaife make an ally lid with one already present) which can also be used to get the pela extraction pipe in.
If the gearbox has to come out then it will enable you to remove and examine clutch components and oil seals and replace if the mileage is reasonable or condition is suspect. Whilst box is out also prop shaft u/j's. A lot to look at but peace of mind and removal further down the line not required.
The Lidl 12V oil pumps that have been mentioned on previous threads do a great job of extracting the old oil and pumping in fresh through the fill hole.
Not sure if they're available at the moment but this is the same thing.
The gearshift on the right of your pic is the Quaife Quickshift, and should be super-smooth in action.
It doesn't have an interference pivot. Instead, you can alter the throw of the lever by reversing the position of the spherical bearing in its housing. Note that this is not generally needed a 7 as the standard throw is normally fast enough.
Quaife's advice on lubricating the spherical bearing is "don't" -- it already runs in a low-friction housing (PTFE or similar). But it's certainly worth checking that it does move freely, especially as it's exposed to road dirt and water. For info on how to dismantle it, see this Guide.
Clutch drag is a possibility, but as you say your bite point is already high, probably unlikely. My money would be on something internal in the box. A call to Phil Stewart at Road & Race Transmissions might shed some light.
I'm with Nigel at #15 - took my 6 speed out (basically your box with a bit of doodads) and rebuilt it but still had the sticky shift, reset the detent spring assembly as per #15 and night and day difference its like a rifle bolt now and super slick.
Also....(and I fully expect to get hung by our club guys on here who know way more than me).......The guy who rebuilt it swore by straight 40 engine oil only, nothing else......
Could we make the execution really neat so I dont suffer gentlemen? :)