Ah, the question of 'German gold'. This has been a heated topic since the accusations were first raised in 1917 and the details have never been less than murky.

The most important point is that at least some German funds did reach the Bolsheviks and other dissident groups. German sources are clear on this. It's worth quoting one key Foreign Ministry telegram at length. Emphasis has been added.

The State Secretary to the Foreign Ministry Liaison Officer at General Headquarters

3 December 1917

The disruption of the Entente and the subsequent creation of political combinations agreeable to us constitute the most important war aim of our diplomacy. Russia appeared to be the weakest link in the enemy chain. The task therefore was gradually to loosen it, and, when possible, to remove it. This was the purpose of the subversive activity we caused to be carried out in Russia behind the front — in the first place promotion of separatist tendencies and support of the Bolsheviks. It was not until the Bolsheviks had received from us a steady flow of funds through various channels and under different labels that they were in a position to be able to build up their main organ, Pravda, to conduct energetic propaganda and appreciably to extend the originally narrow basis of their party. The Bolsheviks have now come to power; how long they will retain power cannot be yet foreseen. They need peace in order to strengthen their own position; on the other hand it is entirely in our interest that we should exploit the period while they are in power, which may be a short one, in order to attain firstly an armistice and then, if possible, peace.

[The remainder of the telegram goes on to spell out potential avenues that Germany might follow to exploit the new situation.]

[Richard von] Kuhlmann

This funding wasn't limited to the Bolsheviks and persisted at least into the early months of 1918. But that's where the clarity ends. Estimates as to the sums provided vary wildly and there's no real indication as to the mechanism of transfer (although it was likely through Stockholm). To complicate things further, the initial charges of conspiracy with Berlin, first presented by the Provisional Government in July 1917, have been shown to be false and based on forged telegrams.

We also have to reckon with the perspective of the sources. Despite Kuhlmann's spin, the idea that German funds were responsible for the Bolsheviks' upturn in fortunes can be safely dismissed. This is far more convincingly explained by the broader trends of 1917, as the country polarised and fell apart. Similarly, ideas of Lenin being a 'German spy', acting on orders from Berlin, seems even more implausible.

Sources

The telegram comes from the very useful Germany and Revolution in Russia 1915-1918, edited by Z Zeman. Semion Lyandres' The Bolsheviks' German Gold Revisited reviews the allegations of 1917.