Just posting this for future reference.  Don't know if one of them fits yours.  Get the number off of your part.

https://www.summitracing.com/search?SortBy=BestKeywordMatch&SortOrder=Ascending&keyword=Mallory Replacement E-Spark Modules

  On 2/3/2023 at 9:36 PM, Zed Head said:

I would just focus on the MSD and the Mallory parts and the coil to start.  Look for signs of overheating, clean things up, assess the quality of the parts.  Be careful moving things around the Mallory module might be adjustable.

p.s. I didn't really study your pictures before.  Looks like you have the full Mallory distributor.  Not sure if you can get replacement parts for those.

Yes full Mallory distributor...I don't know I am tempted to just bypass the MSD and get a new distributor. Which distributor do you recommend? 

There are many opinions on distributors. However, keep in mind that you'll need to learn about how your car is wired now before you start to load the parts cannon. Otherwise, I can pretty much guarantee you'll have other problems you'll be chasing.

1. ZX distributor: Easy to implement, but conventional wisdom says you'll have tach issues. (Running this in my 260Z. Keep in mind it has a different tach than the 240Z.) Also need 280ZX distributor mount. 
2. Stock 240Z distributor: Easy to implement, but you'll have to learn how to set gap and dwell. I'm not sure about the reliability of dwell meters currently available on the market. May need a 240Z distributor mount.
3. Stock 240Z distributor with Pertronix: Easy to implement, but some people question reliability. (Running this in my 240Z.)
4. 280Z distributor with HEI: More knowledge needed for wiring. Need to have a heat sink on the HEI. Easy to replace failed modules. May have tach issues. Also need the 280Z distributor mount.
5. 123 Ignition: Higher price. May need to tweak the spark curve.

Just don't expect to swap out anything quickly.

If you read around you'll find that the Mallory distributor seems to be of high quality.  I posted a link to a site that might have replacement ignition modules/trigger sensors (the red part inside the distributor).  Z car distributors aren't a "buy new and replace" part anymore.  They all take some extra work and many of the options don't have the best advance curves for the engines.

After doing some reading it looks like if you do decide to disconnect the MSD module then you'll have to use a ballast resistor to avoid damaging the Mallory module.  They were developed before current control technology was incorporated in to the modules.  So, don't just disconnect the MSD and run it, or you might burn up the Mallory module.

So, no easy routes to a fix.  If you do buy a new distributor and use it with the MSD and find that you still have the problem at least you'll have a spare.

You could probably replace the MSD with a GM HEI module as a cheap test.  But, still takes some electrical knowledge.  We could go round and round for quite a while.

I ran a Mallory Unilite conversion in an old Mustang years ago, and the Unilite module would eventually get hot enough to quit working.  Using some sort of heat sink grease between the module and distributor plate would usually fix the issue.  I also used thin fiber washers around the 2 module screws to further isolate it from the heat, and another washer under the outside edge so it kind of sat on a thin bed of grease, and kept it level.  It looks like new replacement modules now come with that grease.  Might be a cheap fix to try.