Trouble getting in first gear when car is hot

Sounds a lot like the clutch centre plate is breaking up or has oil on it so it is sticking to flywheel face or pressure plate.

Check and replace as needed.

While I agree that Solar Mike's answer is a possibility, you. might check the simple and inexpensive things first.

1. Try changing the transmission oil/fluid. Sometimes this works wonders especially on an older/high-mileage car.

2. Check the shift linkage for wear, damage, or misalignment. Adjust or replace as needed.

If a seal in the clutch master or slave cylinder is worn, air can enter the clutch hydraulic line. The effect on operation would seem the same as what happens when you don't depress the clutch pedal far enough, i.e., hard shifting into first or reverse. It could also get worse in a hot vehicle because heat would cause a bubble of air to expand and seem like a bigger bubble.

You can bleed your clutch hydraulic system. The procedure is similar to bleeding brakes, and if you do it yourself, the cost is near zero.

Things that may have similar effects:

1. Clutch cable (if cable-operated) misregulated or near-breaking.

2. Clutch hydraulic cylinders and tubing leaky. The master cylinder can leak back into the hydraulic fluid tank and this can be completely undetectable.

Both of the above can be temperature-dependent because the clutch disk somewhat swells when repeatedly operated and heated.

3. Clutch fork cracked. I had one on a different car. It made me, my wife and my mechanic mad. When hot, it used to bend more than when cold. The mechanic was able to weld the crack after sending me a nice photo.

4. Gearbox overheating. Check the gearbox oil level. Check the presence of the heat shields between the exhaust pipe and the gearbox.

5. Gearbox sagging from its place because of aged rubber elements.

A mitigation measure (when the 1st or the reverse doesn't get in): engage 2nd or 3rd first and then quickly 1st or reverse without releasing the clutch pedal.

Or you can even start from 2nd.

I learned to drive in a 1990 Peugeot which quite commonly did this.

First off, as there is no grinding of gears, it is likely that the cogs in the gearbox are not turning when you are trying to engage them.

The second thing to keep in mind is that you are talking about automotive technology which is now over 30 years old and therefore doesn't have as much of the assistive features of more modern cars.

What used to happen with my old Peugeot was that gear cogs would meet each other unevenly, that is tooth-to-tooth or gap-to-gap rather than nicely tooth-to-gap. First and reverse were always the gears which it would happen with most often as they are the lowest ratio gears in the box.

So what can you do? Well my solution was to press the clutch pedal all the way to the floor and let it all the way back up, then do this again before then pushing the clutch down one final time and engaging the gear. This seemed to nudge the cog around enough to allow the gear to then engage.

This may or may not work for you, and it may or may not be the actual reason (I would say there isn't enough info for a definitive diagnosis) but given as all other answers involve some work and money, and this you can try with no risk to yourself or your machine, then why not give it a go? Let me know how you get on!

Quick fixes - Sorry I do not know the specifics of this vehicle but here are two universal tips for easier driving on this era of manual transmission without making repairs.

Reverse - A lot of manual transmissions don't have synchronizers for reverse. This means it is up to you to effectively get the gear aligned with the shaft, but it's easy. Take your foot off the brakes and let the car roll a bit as you are pushing the gear lever towards reverse... eventually the gears will align perfectly and it should slip in easily.

First - Sometimes synchronizers get worn or take awhile to spin up the shaft speed to match. For me, it helped even to understand this process was happening. In my 90s vehicle I would push the gear selector to where it was 'waiting' to shift into first and I could eventually even hear this process where the gear & shaft speeds were matching up and then suddenly it slipped into place with no extra effort. First gear is where this is most necessary & the delay is most pronounced. So you learn to mind (well, not mind) the delay. Push towards first & let the things do their magic. Maybe it's not 'hard' to get it into first gear, it just takes a little more patience than the other gears.

If the synchronizers are completely shot you can pump the gas when the clutch is out without a gear selected & it should speed up the shaft. Then immediately depress the clutch and the gear selection should be easier.