The CETME-L was Spain's replacement for the CETME Modelo C, which was the 7.62x51mm rifle that was essentially adopted by Germany as the G3 in the 1950s. By the 1980s Spain needed to move to the new NATO standard caliber, 5.56x45mm. A domestic design was preferred, so rather than but HK-93 rifles from Germany the Spanish military opted to bring back a development project that had begun back in 1971.
The CETME Modelo L uses the exact same operating system as the Modelo C and the HK 91/93, but because its design was run independently by Spain it shares few interchangeable parts. Most notably, the cocking handle tube and receiver top have a square profile, rather than round. The magazine well was intended to use STANAG magazines, but was not particularly well designed and has a very steep and abrupt feed angle. This, combined with quality control issues in rifle and magazine manufacture led to substantial reliability problems.
The final development was completed between 1982 and 1984, with production beginning in 1986 and the full run or about 100,000 rifles finished in 1991. By 1996 the deficiencies with the rifle were clear, and the Spanish military held replacement trials, which would result in the H&K G36E being adopted in 1999 to replace the Modelo L.
The CETME-L design, if built correctly, is a reasonably good one, although rather old-fahsioned by the late 1980s. It lacked the modularity to allow use of modern optical sights, lasers, attached grenade launchers, and other accessories that were becoming common. This is likely due to the design originating more than a decade earlier - had it been introduced in the early 1970s it would have been much more timely.
Thanks to Hill & Mac Gunworks for letting me take a look at this rifle!