Here is a guide for you to look through
Personally I would look at the gear linkage cables and see if those are as described below
not sure if there is an adjustment for the clutch adjustment is possible.
If this was due to the clutch it would have been high bite point previously. Proving that the clutch has been heavily used this may indicate to you if that is the case?
I also include this that could be useful for you :-
How to Diagnose A Bad Clutch - EricTheCarGuy
Suspect clutch adjustment
If the gears are hard to shift from neutral to first when the engine is running and also from first to second or second to third while accelerating, you could suspect the clutch adjustment. What’s happening is that the clutch is not releasing fully when you press it and hence there’s still some pressure on the gearbox, making it difficult for you to shift gears.
How to fix: If you have a cable-linked clutch, it is easy to adjust clutch play. There is an adjustment nut at the point where the clutch cable meets the clutch actuating lever at the bottom of the engine. TIghen it to reduce clutch play. If you have a hydraulic clutch in your car (some larger capacity diesel cars and petrol cars have this), you will need to get the slave cylinder inspected. Also check for the level of clutch/brake fluid in the reservoir. If it’s low, there may be a leak in the slave cylinder which will need to be replaced. This could be slightly expensive.
Gear linkage bushes are worn
If the gear lever does not slot surely into a gear and feels rubbery then it’s a problem with the bushes at the bottom of the gear lever. This could have become hard and brittle, which will make it tough to change gears. Also check the gear linkage mechanism. There are two kinds of gear linkage mechanisms – cable shift or rod shift. The rod shift is also called a “direct linkage” and is more durable. Cable shift mechanisms however feel smoother and are used on front wheel drive cars mainly, as it’s easier to package.
How to fix: Get the bushes replaced. Sometimes, you may also need to change the gear cable (in a cable shift mechanism) if the cable has become hard with age.
Gears make grinding sound on quick shifts
If the gears do not slot easily and instead make a grinding sound on quick shifting between one gear and another, you may have a larger problem on your hands. The gearbox has synchronizers in it which are collars that match the speeds of various gears with each other, so that they slot in at any speed making it convenient to drive instead of having to double de-clutch to match engine and gearbox speeds (early gearboxes were non-synchromesh). If you are very rough with the gears, over time, these synchronizers can wear off or worse still the gears could lose a couple of teeth, which will lead to difficulty in shifting and grinding noises.
How to fix: If you encounter constant grinding noises, you will need to open up the gearbox and get the gears and synchronizers checked and replaced as needed. This is an expensive repair
