I have known this not always a good idea and communicate it with folks I talk to, most don't seem to care. What have you all heard or seen? It is obvious that some LED clusters will not work, though some are a great fit in older incandescent fixtures.

This from Hella:

RETROFITTING INCANDESCENT NAV LAMPS
WITH LED BULBS IS UNSAFE, ILLEGAL

"With all the power-saving and longevity benefits of LED lights, it's easy to see why boat owners replace traditional light bulbs with LEDs. But doing so with navigation lights can violate the fixture's certifications. This has serious consequences, as US Inland Navigation Rules and International Navigation Rules carry the force of federal law.
"A certified navigation light fixture is a combination of a specific lens, a specific bulb and the necessary foundation and wiring. The boat owner or operator must ensure that when bulb replacement is necessary, only the original type bulb is used," said Phil Cappel, chief of the US Coast Guard's Recreational Boating Product Assurance Branch. "Any substitutions can result in the light no longer meeting the Navigation Rule requirements."
A wide variety of replacement bulbs are available, including LED bulb conversion kits. Simply finding one that fits the fixture won't assure the boater of a properly certified navigation light, unless the lamp manufacturer has third party-certified it for their own lamp. Cappel notes that compliance with the Navigation Rules is the boat operator's responsibility, not the bulb manufacturer's.
Industry specifications and certifications are in place for safety. Though seemingly simple, the red, white and green navigation lights are thoroughly tested by a third party for light intensity, color, angles of visibility, corrosion and temperature. "The lamp assemblies are designed
and tested with a specific light source," said Brian Goodwin, technical director for the American Boat and Yacht Council (ABYC).
Precise tests determine if light reaches nautical mile requirements. Light output must also be sharp at the edges and smooth across the arcs of visibility. This prevents light from appearing to flash like a buoy rather than project consistently when the boat rotates and rocks.
Goodwin notes that there are other causes of failure if the owner replaces a bulb with one other than the original type. For example, LEDs installed in a housing intended for a hot bulb may dim unexpectedly. "Unless approved and tested by the light fixture manufacturer, LED retrofit bulbs do not belong in navigation lights," he said.
"Flaunting the law risks lives, insurance and liability," said Jeremy Singleton, Hella marine global manager. "The USCG and ABYC take navigation lighting very seriously. They are considered life-saving devices to avoid collisions at sea and on inland waterways."
The simple solution for owners wishing to upgrade to LED navigation lights is to replace the entire light assembly with a certified product. This ensures their navigation lights are safe, and legal.